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ASE A1 practice questions

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Question 1General Engine Diagnosis

During a dry compression test on a gasoline engine, which procedure gives the most accurate results?

  1. All spark plugs installed and the throttle held wide open
  2. One spark plug removed at a time with the throttle at idle position
  3. All spark plugs removed and the throttle held fully closed
  4. All spark plugs removed and the throttle held wide open Correct answer.

Explanation

Removing all plugs lets the starter crank the engine at a consistent speed without fighting compression from the other cylinders, and propping the throttle open lets each cylinder fill completely with air. The reading then reflects only that cylinder's sealing ability against a full air charge.

Question 2General Engine Diagnosis

An engine burns oil and produces a puff of blue-gray smoke right after a cold start that clears within a few seconds. Which is the most likely cause?

  1. A stuck-open PCV valve
  2. Worn piston rings
  3. Worn valve stem seals Correct answer.
  4. A leaking rear main seal

Explanation

Oil that seeps past worn valve stem seals while the engine sits is drawn into the cylinders and burned during the first few firing cycles, producing a brief puff at startup that then clears. Ring wear produces continuous smoking, particularly under acceleration and load.

Question 3General Engine Diagnosis

An engine takes an unusually long time to reach normal operating temperature and heater output stays lukewarm. Which is the most likely cause?

  1. A radiator cap that does not hold pressure
  2. A water pump with a worn impeller
  3. A fan clutch that is seized engaged
  4. A thermostat stuck open Correct answer.

Explanation

A thermostat that stands open lets coolant circulate through the radiator from the moment the engine starts, so the coolant is constantly being cooled and warm-up is slow. Heater output suffers because coolant never reaches normal temperature.

Question 4General Engine Diagnosis

A sharp metallic rattle from the engine under acceleration that disappears as soon as the throttle is released is best described as:

  1. Rod bearing knock
  2. Spark knock (detonation) Correct answer.
  3. Valve lifter tick
  4. Piston slap

Explanation

Detonation occurs when the end gas in the cylinder ignites spontaneously under high pressure and temperature, producing a sharp metallic rattle that tracks directly with throttle application and load. Releasing the throttle drops cylinder pressure and the noise stops immediately.

Question 5General Engine Diagnosis

An engine idling at sea level shows a steady vacuum gauge reading of about 11 in-Hg. Which does this most likely indicate?

  1. An intake vacuum leak Correct answer.
  2. Worn valve guides
  3. Normal engine condition
  4. A restricted exhaust system

Explanation

A healthy engine at sea level normally idles at roughly 17 to 22 in-Hg, so a steady reading well below that range means the intake charge is being diluted by air that bypasses the throttle, as with a leaking manifold or hose. Late valve timing produces a similar steady low reading.

Question 6General Engine Diagnosis

A serpentine belt squeals loudly at idle and the noise worsens when the A/C compressor engages. Which is the most likely cause?

  1. A failed tensioner bearing that growls
  2. A glazed or worn drive belt Correct answer.
  3. An overcharged A/C system
  4. A worn water pump seal

Explanation

Squeal is the sound of the belt slipping on its pulleys, and it appears when a load such as the compressor is applied. Glazing, wear, contamination, or insufficient tension all reduce friction between belt and pulley and produce that slip.

Question 7General Engine Diagnosis

Black smoke from the tailpipe of a fuel-injected engine indicates:

  1. Oil entering the combustion chamber
  2. A restricted catalytic converter
  3. Coolant entering the combustion chamber
  4. An excessively rich air/fuel mixture Correct answer.

Explanation

Black smoke is particulate carbon left over from fuel that could not be fully burned, which points to too much fuel for the air available. Blue smoke indicates oil consumption and white vapor indicates coolant entering the cylinders.

Question 8General Engine Diagnosis

The oil pressure warning light on a vehicle comes on at hot idle and goes out as soon as engine speed increases. Which is the most likely cause?

  1. Worn engine bearings or a worn oil pump Correct answer.
  2. The oil pressure sending unit is unplugged
  3. The crankcase is overfilled by one quart
  4. The oil filter is new and the oil is cold

Explanation

Hot oil is thin, and enlarged bearing clearances let it escape faster than a worn pump can supply it at low speed, so pressure falls below the switch threshold at idle and recovers as pump speed rises. This speed-dependent pattern is the classic signature of internal wear.

Question 9General Engine Diagnosis

A cylinder leakage test is performed with the piston at TDC on the compression stroke and air is heard escaping from the radiator filler neck. Which is the most likely cause?

  1. Worn piston rings
  2. A leaking head gasket Correct answer.
  3. A burned exhaust valve
  4. A leaking intake valve

Explanation

Air can only reach the cooling system by crossing from the combustion chamber through a breach into a coolant passage, which means a failed head gasket or a cracked casting. Ring leakage escapes through the crankcase, intake valve leakage out the throttle body, and exhaust valve leakage out the tailpipe.

Question 10General Engine Diagnosis

A dry compression test reads 90 psi on one cylinder, and adding a teaspoon of oil raises the reading to 135 psi. This indicates:

  1. A leaking head gasket
  2. Worn piston rings Correct answer.
  3. A burned exhaust valve
  4. A worn camshaft lobe

Explanation

The added oil temporarily seals the gap between the rings and the cylinder wall, so a large jump in the wet reading proves the compression was escaping past the rings. Leakage past valves or the head gasket is unaffected by oil in the bore.

Question 11General Engine Diagnosis

A PCV valve that is stuck in the open position will most likely cause:

  1. No effect on idle quality
  2. Higher crankcase pressure and oil leaks
  3. Black smoke and a rich exhaust
  4. A lean idle and rough running Correct answer.

Explanation

A PCV valve stuck open flows more crankcase vapor than the PCM has accounted for, adding unmetered air downstream of the throttle and leaning the idle mixture. Because the leak is a large share of total airflow at idle, the engine may idle rough or stall.

Question 12General Engine Diagnosis

A backpressure test reads 4 psi at the upstream oxygen sensor port with the engine held at 2500 rpm. How should this reading be interpreted?

  1. Low, indicating an exhaust leak
  2. Slightly high but within specification
  3. Normal for a healthy exhaust system
  4. Excessive, indicating a restriction Correct answer.

Explanation

The commonly accepted limit is roughly 1.5 to 2 psi at 2500 rpm, so a reading of 4 psi shows the exhaust cannot flow freely. The restriction is typically a plugged catalytic converter or a collapsed pipe, and it shows up as low power and manifold vacuum that falls as speed increases.

Question 13General Engine Diagnosis

Long-term fuel trim reads plus 22 percent at idle on a mass-airflow-equipped engine and falls to plus 5 percent at 2500 rpm. Which is the most likely cause?

  1. A leaking fuel injector
  2. A vacuum leak Correct answer.
  3. A coolant sensor reading colder than actual
  4. A restricted fuel filter

Explanation

Unmetered air entering through a leak is a large fraction of total airflow at idle, when manifold vacuum is highest, so the PCM adds a lot of fuel there. As airflow rises with engine speed the leak becomes a smaller share and the correction returns toward normal.

Question 14General Engine Diagnosis

Which test best isolates which cylinder is misfiring on a distributorless ignition engine?

  1. A compression test on all cylinders
  2. A charging system output test
  3. A fuel pressure leak-down test
  4. A cylinder power balance test Correct answer.

Explanation

A power balance or contribution test cancels each cylinder's firing in turn and watches the change in cranking or running speed, so a dead cylinder shows little or no rpm change. This pinpoints the faulty cylinder before further testing of spark, fuel, and compression.

Question 15General Engine Diagnosis

An engine overheats in stop-and-go traffic but runs at normal temperature on the highway. Which is the most likely cause?

  1. An inoperative electric cooling fan Correct answer.
  2. A thermostat stuck closed
  3. A worn water pump impeller
  4. A leaking head gasket

Explanation

At highway speed ram air moves enough air through the radiator to cool the engine, but at low speed cooling depends entirely on the fan pulling air through the core. A fan that never runs therefore causes overheating only when the vehicle is slow or stopped.

Question 16General Engine Diagnosis

An engine has a light metallic rattle for the first minute after a cold start that fades as it warms up. Which is the most likely cause?

  1. Excessive piston-to-bore clearance Correct answer.
  2. A worn main bearing
  3. A cracked flywheel
  4. A collapsed lifter that stays collapsed

Explanation

Pistons are machined with clearance for thermal expansion, and when that clearance is excessive the skirts rock in the bores and rattle until the pistons grow with heat. The noise disappears as clearances close at operating temperature.

Question 17General Engine Diagnosis

An engine loses coolant with no visible external leak, and bubbles rise continuously in the radiator with the cap off and the engine running. Which test best confirms the diagnosis?

  1. A cooling system pressure test
  2. Testing the coolant for combustion gases Correct answer.
  3. A thermostat opening test
  4. A cylinder compression test

Explanation

A block tester draws air from the radiator through a chemical that changes color in the presence of combustion byproducts, which proves exhaust gas is being forced into the cooling system. That is direct evidence of a failed head gasket or a cracked casting.

Question 18General Engine Diagnosis

After a timing belt replacement an engine suddenly idles poorly, has low manifold vacuum, and lacks power. Which is the most likely cause?

  1. The camshaft is off by one tooth Correct answer.
  2. The PCM lost its adaptive memory
  3. The spark plug gaps were set too wide
  4. The oil was overfilled

Explanation

A camshaft installed one tooth off shifts every valve event relative to the crankshaft, so the intake valve opens late and manifold vacuum drops along with low-speed power. Wide gaps or lost adaptive memory do not change measured vacuum.

Question 19General Engine Diagnosis

A deep, dull knock that is loudest at hot idle, increases under load, and comes with low oil pressure is most likely:

  1. A valve lifter tick
  2. A worn rod or main bearing Correct answer.
  3. An exhaust leak at the manifold
  4. A loose accessory drive belt

Explanation

Enlarged bearing clearance lets the journal hammer against the bearing shell each time it is loaded, producing a heavy knock, and the excess clearance also drops oil pressure. The knock is worst when the oil is hot and thin and under load.

Question 20General Engine Diagnosis

A spark plug from one cylinder is dry and heavily sooted black while the other plugs show normal light tan coloring. Which is the most likely cause?

  1. Coolant entering that cylinder
  2. A lean condition from a vacuum leak
  3. A rich mixture in that cylinder Correct answer.
  4. Oil being burned in that cylinder

Explanation

Dry black carbon fouling with a fuel smell means too much fuel or incomplete combustion in that bore, such as a leaking injector, restricted airflow, or a persistent misfire. Coolant leaves a steam-cleaned plug and burning oil leaves wet, shiny black deposits.

Question 21General Engine Diagnosis

During a cylinder leakage test on cylinder 3, air is heard escaping from the spark plug hole of cylinder 2. Which is the most likely cause?

  1. A burned intake valve
  2. A blown head gasket Correct answer.
  3. A cracked exhaust port
  4. Worn piston rings

Explanation

Air can only travel from one bore to the next through a breach in the head gasket or a crack in the deck between the cylinders. Leakage past valves or rings escapes to the intake tract, the exhaust, or the crankcase instead of into another cylinder.

Question 22General Engine Diagnosis

A vacuum gauge connected to an engine at steady idle shows the needle fluctuating rapidly between about 15 and 19 in-Hg. Which is the most likely cause?

  1. Late ignition timing
  2. A sticking valve or weak valve spring Correct answer.
  3. A leaking intake manifold gasket
  4. A restricted exhaust system

Explanation

Rapid needle flutter at steady idle means one or more cylinders are contributing unevenly, which happens when a valve sticks, seats poorly, or is held open by a weak spring. Steady low readings point to leaks or retarded timing, and a reading that falls as speed rises points to exhaust restriction.

Question 23General Engine Diagnosis

A high-mileage engine sets a camshaft-to-crankshaft correlation code, idles roughly, and rattles briefly at cold start-up. Which is the most likely cause?

  1. Low fuel pressure at cold start
  2. A stretched timing chain Correct answer.
  3. A clogged PCV valve
  4. A faulty crankshaft position sensor

Explanation

As the chain stretches, the camshaft lags behind the crankshaft, so the PCM sees cam and crank signals that no longer agree and sets a correlation code. The slack chain also slaps its guides on a cold start until oil pressure takes up the tensioner.

Question 24General Engine Diagnosis

An engine pushes oil out of the dipstick tube and has excessive crankcase pressure even though the PCV valve and hoses are new and correctly routed. Which is the most likely cause?

  1. A clogged air filter element
  2. A faulty oil pump relief valve
  3. Excessive blow-by from worn rings Correct answer.
  4. An overfull crankcase

Explanation

When the rings and cylinder walls no longer seal, combustion pressure leaks into the crankcase faster than the PCV system can evacuate it, forcing oil out of the dipstick tube and seals. A verified-good PCV system isolates the source to the engine's internal sealing.

Question 25General Engine Diagnosis

A vehicle misfires only under heavy load at operating temperature. Compression and cylinder leakage tests on the suspect cylinder are within specification. Which is the most likely cause?

  1. A restricted fuel injector at idle
  2. An ignition coil breaking down under load Correct answer.
  3. An intake manifold vacuum leak
  4. A worn camshaft lobe

Explanation

High cylinder pressure under load raises the voltage needed to jump the plug gap, so a coil, boot, or plug with weakened insulation arcs internally and misfires. Because the mechanical tests are normal, the fault lies in the ignition secondary circuit.

Question 26General Engine Diagnosis

A distributorless ignition engine cranks at normal speed but will not start, and a spark tester shows no spark at any cylinder. Which is the most likely cause?

  1. The electric fuel pump is not running
  2. No crankshaft position sensor signal Correct answer.
  3. One coil-on-plug coil has failed open circuit
  4. Fuel injectors are not receiving a pulse

Explanation

On a distributorless system the PCM needs a crankshaft position signal before it will trigger any coil or fire the injectors, so a missing signal kills spark everywhere at once. Loss of one coil affects only that cylinder, and fuel-system faults do not eliminate spark.

Question 27General Engine Diagnosis

An engine emits a puff of blue-gray smoke for a few seconds after an overnight soak, then runs clean with no smoke under load. Which is the most likely cause?

  1. Worn piston rings and cylinder walls
  2. Leaking intake manifold coolant passage
  3. Worn valve guides and stem seals Correct answer.
  4. A PCV valve stuck in the open position

Explanation

Oil seeps past worn valve stem seals and guides while the engine sits, pooling on top of the valves; it burns off in the first seconds after start-up and then the smoke stops. Ring wear produces smoke that continues under load, and coolant produces white vapor.

Question 28General Engine Diagnosis

A scan tool on an engine with a two-wire ECT sensor displays minus 40 degrees F with the key on and the engine cold. What is the most likely effect on engine operation?

  1. No effect, because the sensor only drives the temperature gauge
  2. Lean mixture and reduced idle speed
  3. Rich mixture and elevated idle speed Correct answer.
  4. The injectors are disabled and the engine will not start

Explanation

An open or shorted sensor circuit drives the reported temperature to an extreme cold value, so the PCM adds fuel for cold operation and raises idle speed. Fuel trim will show a rich correction until the circuit is repaired.

Question 29General Engine Diagnosis

A vehicle spark knocks lightly during light-throttle acceleration at normal operating temperature. Base ignition timing, fuel octane, and cooling system operation are all correct. Which is the most likely cause?

  1. A restricted exhaust system
  2. A cooling system that runs too cold
  3. An inoperative EGR valve Correct answer.
  4. A leaking intake manifold gasket

Explanation

Exhaust gas recirculation dilutes the incoming charge and lowers peak combustion temperature, which is what suppresses light-load knock. When the EGR valve does not flow, combustion temperatures rise and the engine knocks under light acceleration.

Question 30General Engine Diagnosis

A vehicle with an automatic transmission has a vibration felt in the seat and steering wheel at idle in gear that largely disappears when engine speed is raised or the transmission is shifted to neutral. Which is the most likely cause?

  1. A worn constant-velocity driveshaft joint
  2. A secondary ignition misfire on one cylinder
  3. A worn or collapsed engine mount Correct answer.
  4. An out-of-balance wheel and tire assembly

Explanation

A collapsed hydraulic mount loses its ability to isolate the normal torque reaction and vibration when the engine is loaded in gear, and the vibration fades once load is removed. Chassis and driveline faults vary with vehicle speed, not with engine load at a standstill.

Question 31General Engine Diagnosis

A customer complains of weak heater output. After a 20-minute drive the scan tool shows coolant temperature stabilizing at about 150 degrees F, and the PCM has set a coolant-temperature-below-regulating-temperature code. Which is the most likely cause?

  1. Water pump impeller eroded
  2. Thermostat stuck open Correct answer.
  3. Pressure cap holding less than its rated pressure
  4. Thermostat stuck closed

Explanation

A thermostat that stays open lets coolant circulate through the radiator continuously, so the engine never reaches its designed operating temperature and the heater core receives lukewarm coolant. The below-regulating-temperature code is set specifically when the engine fails to warm up in a set time.

Question 32General Engine Diagnosis

A distributorless engine cranks but will not start. Spark is strong at every plug, injector pulse is present, and fuel pressure is within specification. A compression test shows about 60 psi on all cylinders, dry and wet, against a specification of 150 psi. Which is the most likely cause?

  1. The head gasket is blown between two cylinders
  2. Several valves are bent
  3. The timing chain has jumped Correct answer.
  4. The piston rings are worn out

Explanation

Compression that is uniformly low on every cylinder while spark and fuel are normal points to valve timing, not to wear in one or two areas. A chain that jumps a tooth or more holds valves open during the compression stroke on all cylinders, dropping cranking compression evenly.

Question 33General Engine Diagnosis

A vehicle with a distributor-type ignition runs well until it reaches operating temperature, then the engine stalls and will not restart until it cools for 20 to 30 minutes. During the no-start, a spark tester shows no spark at any plug. Which is the most likely cause?

  1. A failing ignition control module Correct answer.
  2. An ignition switch with an open circuit
  3. A restricted fuel filter that cannot flow enough volume
  4. A fuel pump relay with high resistance

Explanation

An electronic component with a thermal intermittent opens when it heat-soaks and works again after it cools, which explains the temperature-linked pattern. Since spark is absent during the fault, the ignition control module or pickup inside the distributor is the prime suspect.

Question 34General Engine Diagnosis

A port fuel-injected vehicle requires a long crank to start after a 15-minute hot soak, but starts immediately from cold. Key-on fuel pressure is at the 50 psi specification, but it falls to 10 psi within two minutes after the pump stops. Which is the most likely cause?

  1. Leaking fuel injectors Correct answer.
  2. A pressure regulator stuck closed
  3. A restricted fuel filter element
  4. A fuel pump with low maximum pressure

Explanation

The system must hold pressure after shutoff; a rapid bleed-down means fuel is escaping past an injector or the pump check valve. On a hot soak the rail drains and vapor forms, so the pump must re-prime the rail before the engine can fire.

Question 35Cylinder Head and Valve Train Diagnosis and Repair

On a mechanical valvetrain, where is valve clearance measured?

  1. Between the retainer and guide
  2. Between the pushrod and lifter
  3. At the valve tip and rocker arm pad Correct answer.
  4. Between the valve face and seat

Explanation

Valve clearance is the gap in the load path between the rocker (or cam follower) and the valve stem tip; it is set with a feeler gauge and allows for thermal expansion.

Question 36Cylinder Head and Valve Train Diagnosis and Repair

A cylinder head deck is checked for warpage using which tools?

  1. A straightedge and feeler gauge Correct answer.
  2. A dial indicator on a magnetic base
  3. An outside micrometer
  4. A telescoping gauge

Explanation

Deck flatness is checked by placing a straightedge across the head in several directions and trying to slip a feeler gauge under it; the largest gauge that fits indicates the warpage.

Question 37Cylinder Head and Valve Train Diagnosis and Repair

What is the primary job of a positive valve stem seal?

  1. Keep the valve from rotating
  2. Increase spring seat pressure
  3. Control oil past the guide Correct answer.
  4. Center the valve on its seat

Explanation

The stem seal wipes the stem and limits oil traveling down the guide into the port, where it would burn and produce blue exhaust smoke.

Question 38Cylinder Head and Valve Train Diagnosis and Repair

What is the function of the valve spring?

  1. Close the valve against its seat Correct answer.
  2. Dampen camshaft harmonics
  3. Seal combustion pressure
  4. Rotate the valve during operation

Explanation

The spring returns the valve to its seat and keeps it there throughout the cycle; without adequate pressure the valve can float or bounce.

Question 39Cylinder Head and Valve Train Diagnosis and Repair

Which symptom most directly indicates an internal coolant leak from a failed head gasket?

  1. Low fuel pressure
  2. Coolant in the engine oil Correct answer.
  3. A lifter tick when cold
  4. Blue smoke only at startup

Explanation

A breach between a coolant passage and an oil passage cross-contaminates the fluids, producing milky oil or coolant loss with no external leak.

Question 40Cylinder Head and Valve Train Diagnosis and Repair

What valve face angle is most common on production gasoline engines?

  1. 15 degrees
  2. 45 degrees Correct answer.
  3. 60 degrees
  4. 30 degrees

Explanation

A 45-degree face with a matching seat is the standard production combination; 30-degree seats are sometimes used on intake valves to improve flow.

Question 41Cylinder Head and Valve Train Diagnosis and Repair

Before installing a timing belt on an OHC engine, which of these must be aligned?

  1. Valve stem heights
  2. Spark plug gaps
  3. Pushrod lengths
  4. Timing marks Correct answer.

Explanation

The crankshaft and camshaft timing marks must line up with the manufacturer's marks so valve events stay synchronized with piston position.

Question 42Cylinder Head and Valve Train Diagnosis and Repair

How is a hydraulic lifter with a non-adjustable rocker set to the correct preload?

  1. Spring installed height
  2. Rocker arm ratio
  3. Zero lash plus specified turns Correct answer.
  4. Valve lash of 0.030 in. (0.76 mm)

Explanation

The adjuster is tightened until pushrod spin resistance just disappears (zero lash) and then turned the specified number of turns to set plunger preload.

Question 43Cylinder Head and Valve Train Diagnosis and Repair

Excessive valve stem-to-guide clearance will most likely cause which condition?

  1. Increased valve lift
  2. Advanced ignition timing
  3. Higher spring pressure
  4. Oil use and wobble Correct answer.

Explanation

A worn guide lets the valve rock, which prevents the seal from wiping the stem and allows oil into the port; it also misaligns the valve face with the seat.

Question 44Cylinder Head and Valve Train Diagnosis and Repair

A valve seat contact width measures wider than specification. What is the correct repair?

  1. Replace the valve and guide
  2. Narrow the seat to spec Correct answer.
  3. Shim the spring
  4. Lap the valve longer

Explanation

Seat width is corrected by cutting the seat with the proper angles until the contact band meets the manufacturer's width, then checking concentricity.

Question 45Cylinder Head and Valve Train Diagnosis and Repair

Valve spring installed height is measured between which two points?

  1. Valve tip and guide top
  2. Cam base circle and lifter
  3. Rocker pivot and pushrod
  4. Retainer and spring seat Correct answer.

Explanation

Installed height is the distance from the spring seat in the head to the underside of the retainer with the valve closed; it determines spring pressure.

Question 46Cylinder Head and Valve Train Diagnosis and Repair

Loss of valve control at high engine speed is called what?

  1. Valve recession
  2. Valve float Correct answer.
  3. Valve lash
  4. Valve overlap

Explanation

When spring force cannot keep the follower on the cam at high rpm, the valve loses contact and can bounce on its seat, a condition called valve float.

Question 47Cylinder Head and Valve Train Diagnosis and Repair

A pushrod is found bent during teardown. Which is the most likely cause?

  1. Low fuel pressure
  2. A leaking stem seal
  3. Excessive rocker clearance
  4. A valve stuck in its guide Correct answer.

Explanation

A valve that seizes in its guide stops the valvetrain mid-lift, so the cam or rocker force bends the weakest link, usually the pushrod.

Question 48Cylinder Head and Valve Train Diagnosis and Repair

While adjusting a running hydraulic lifter, what is the final adjustment?

  1. Set lash with a feeler gauge to 0.020 in.
  2. Back off until the pushrod spins freely
  3. Zero lash plus the specified turns Correct answer.
  4. One full turn past coil bind

Explanation

The adjuster is backed off until clatter, then tightened to zero lash and turned the specified additional amount to center the plunger.

Question 49Cylinder Head and Valve Train Diagnosis and Repair

How should torque-to-yield cylinder head bolts be handled?

  1. Torque them cold only
  2. Replace them and torque to angle Correct answer.
  3. Coat them with sealer and reuse
  4. Reuse them if they are not stretched

Explanation

Torque-to-yield bolts are tightened past yield and permanently stretch; they must be replaced and tightened in stages to a torque plus a specified angle.

Question 50Cylinder Head and Valve Train Diagnosis and Repair

During a cylinder leakage test, air escapes from the throttle body. Which is the cause?

  1. Intake valve leakage Correct answer.
  2. A burned exhaust valve
  3. A worn piston ring
  4. A leaking head gasket

Explanation

Air heard at the throttle body is traveling up the intake port, so the intake valve is not sealing against its seat.