If your vehicle is showing engine stalls unexpectedly while idling at a stoplight, here are the most likely causes and the parts you'll need to fix each one.
Carbon buildup blocks the small air passages needed to keep the engine running when your foot is off the gas pedal. This starves the engine of air at idle, causing it to stall.
A cracked hose or loose intake tube lets unmeasured air into the engine, throwing off the air-fuel mixture. This is a very common installation error if a hose is accidentally left disconnected after recent under-hood work.
The sensor that measures incoming air gets dirty or fails, causing the engine computer to calculate the wrong air-fuel mixture. This often results in a rough idle that eventually stalls out.
The valve that recirculates exhaust gases gets stuck open due to carbon buildup. This chokes the engine with exhaust fumes when it desperately needs fresh air at idle.
These sensors tell the computer the engine's internal timing. If they overheat and fail, the computer loses track of the engine's position at low RPMs and shuts off the spark or fuel.
In an automatic transmission, if the torque converter fails to unlock when you stop, it acts exactly like forgetting to press the clutch pedal in a manual car, violently stalling the engine.