Q: Car starts fine sometimes but idles out after pressing the gas.

Hi and thanks for contacting YourMechanic. If you start your engine and it runs fine, then when pushing on the gas pedal then engine starts to rev up and then goes to an idle, this is an issue with the throttle position sensor (TPS), a defective idle air control valve (IAC), or a failed camshaft sensor.

If the engine is trying to stall out during driving conditions, then check the fuel pump for it if it is working. If the fuel pump is working, then check the fuel pressure on the fuel rail and make sure that you are reading 35 psi or more. If you are reading less than 35 psi, then the fuel pump needs replaced or the fuel filter is plugged and needs replaced.

If the fuel pressure is 35 psi or more, then check the exhaust for a plugged muffler or plugged catalytic converter. You can do this by putting something on the exhaust tail pipe and block the exhaust from coming out with the engine running. If the air is a little pressure, then there is a plugged muffler or plugged catalytic converter. If you can remove the muffler, then take it off and recheck the pressure. If the pressure is still low, then the catalytic converter is plugged. If the pressure is high, then the muffler is plugged.

Now, if you have checked all of the possibilities for the engine to have an issue with the idle issue when pressing the gas pedal, then there could be an issue with PCM. To have this all scoped out, I recommend having a local professional diagnose the stalling problem so that this can be appropriately repaired.