P0335 P0300 - 4 cyl

I have replaced a ton of coils on these. And the PT Cruisers. Same engine.

Clean the throttle body and check or replace the idle control valve. Also check or test the throttle position sensor.

bad computer. had the same problem sent mine to auto computer exchange in Davie Fl. they reprogramed it . The problem is gone.

the pcm may have a cracked board, i had an 88 cavalier z24 with the same problem, replced the ecu and it ran fine, the problem is that the boards inside the pcm crack and lose connection, the next time it acts up open the glove box and try tapping on the pcm, if the car responds at all, the pcm is bad

Check your idle control valve...

change fuel filter.if all good .scan it to check the egr valve and idle speed control.or check out ignition system.

I need to get a clear mental picture of what exactly is happening.

With this said, you stated that the car "runs fine" until warmed up.

Q: When you start the car when cold it idles fine?
Q: If you allow the car to idle until "fully" warmed does the car stall?
Q: As the car begins to warm up, Does the RPM fluctuate abnormally?
Q: Does the car Only stall when you press on the gas pedal or does it stall just sitting and idling in addition to pressing the gas pedal?
Q: If you can drive it while cold does the car stall during acceleration when warm or only at Stop Signs / Lights?
Q: If you wait 20min or so, can you start the car again?
Q: How many miles are on the car?

Pour the fuel injection cleaner to it....sounds like the injectors are dirty.....

i would start by checking the spark plugs and leads. if that ok i would think there is a problem with the dispack that the spark plug leads fit to, if its cracked or any rust i would replace.

if this a fuel injected car just check to fuel pressure first.