I just recently developed this problem. I'll start my car and leave it idling in park. Once the engine starts getting warm it'll idle up and down a few hundred rpms. Then as it gets warmer it'll stutter and act like it wants to die then it'll correct itself. Then if I raise the rpms up to around 2500 it'll still stutter as I'm holding at those rpms. Any help on this would be greatly appreciated. Thank you

 

Sounds like an issue with fueling or an oxygen sensor.

When you first start a car and it is in Open Loop the PCM just dumps a bunch of fuel into the engine until the sensors warm up. Then when it enters closed loop, it uses readings from the MAF and O2 sensor to adjust fueling, sounds like when yours enters closed loop it is getting messed up.

 

Okay thanks for that help. I was thinking it was maybe something to do with the ignition but I'll look in the direction you pointed me. I have an off road pipe on it so the rear oxygen sensor is sending a code but I've had that for a long time now with no issues. Maybe I need to invest in an o2 simulator and see if that helps

 

The rear oxygen sensor just reads the cat, shouldn't affect driveability for you.

 

Fuel pressure regulator?