What Causes a Car to Stall When Releasing the Throttle?

[BriellaRose]

The reasons for stalling when releasing the throttle: 1. Fuel pressure too low, air filter clogged, injector atomization leaking, improper idle adjustment, spark plug malfunction, air flow meter failure; 2. Fuel injector inside the engine dripping or clogged, circuit failure or insufficient fuel injection; 3. Throttle carbon buildup issue: The throttle is a control device for engine power, part of the car's fuel supply system. By adjusting the pedal pressure, it controls the engine throttle opening, regulates air intake, and the computer controls fuel quantity, thereby managing engine speed. Additional information: The throttle's function is to control the carburetor's throttle opening to regulate cylinder filling and manage the fuel regulator's metered fuel flow, determining the engine's output power and generating thrust.

[StellaMarie]

I've encountered this issue quite a few times, and in most cases, it's related to problems with the engine's intake system or fuel delivery system. For instance, excessive carbon buildup in the throttle body causing it to stick, or the idle air control valve being clogged with sludge, preventing the ECU from automatically adjusting the air intake. Another possibility is clogged fuel injectors in the fuel system or an aging fuel pump failing to deliver sufficient fuel. Once, while helping a neighbor with their car, I found that the wiring harness of the crankshaft position sensor had worn through, causing intermittent signals and misfiring. For such issues, it's advisable to start by cleaning the throttle body, and remember to ask the mechanic to check for any vacuum leaks while they're at it. For older cars, it's also a good idea to test the spark plugs and ignition coils. A lean air-fuel mixture can also cause the engine to stall when decelerating. I recently applied this approach to an old Camry with good results.

[Dawson]

As a frequent visitor to repair shops, I believe the main focus should be on three key areas: First, the throttle body is as dirty as a pot bottom, causing the flap to return slowly due to sticking; second, the exhaust gas recirculation valve doesn't close tightly, constantly feeding exhaust gases back into the engine; third, the fuel tank ventilation system needs checking—a clogged EVAP charcoal canister can disrupt the air-fuel mixture ratio. Last month, my car had the same issue, and the mechanic used a diagnostic tool to detect abnormal oxygen sensor voltage fluctuations—replacing the sensor fixed it. Additionally, if the mass airflow sensor gets clogged with spider webs, it can cause similar problems. There was a Lexus that had idle surge issues because of this.

[ValerieRose]

Simply put, there's a power disconnection when lifting off the throttle. This is common in direct injection vehicles. A stuck fuel pump pressure relief valve can cause sudden fuel pressure drops. For sensors, focus on checking intake pressure sensor signal drift, or a coolant temperature sensor falsely reporting low temperature causing the ECU to miscalculate fuel delivery. One BMW owner complained about stalling, which turned out to be the variable valve lift system stuck at maximum opening. Another easily overlooked issue: turbocharged vehicles with wastegates stuck in the pressure relief position, causing sudden turbo stall when lifting off the throttle. Recommended troubleshooting sequence: clean carbon deposits → test fuel pressure → read fault codes → check air intake system sealing.