I have an LO3 and it usually runs great, but there are times when the car has been sitting for a while and when I go to start the car (and the engine is still warm) it idles rough. When I give it gas, it sputters and bogs down for a second, then the RPMs shoot up and then immediately sputter back down. After about 15-20 seconds of driving like this, it finally hits high RPMs consistently and everything smoothes out and idles fine and drives completely normal after this. The car ONLY does this when the engine is warm and the temperature outside is in the 90's, and it never lasts more than 30 seconds or so. It doesn't throw any codes either. Could it be the TPS, or maybe the MAT sensor? Tried a and I'm still not sure. Any help would be greatly appreciated!

 

My new motor is doing the same thing, except I have to let it cool all the way down for it to run right. Is your EGR valve and passages clear and working properly? How about our PCV valve?

 

The EGR valve might be the problem, because the Check Engine light does come on every once in a while (because of the EGR valve), but I never did anything about it because it didn't affect anything and I never had any problems until now. I'll check it out and I'll also replace the PCV valve while I'm at it and probably the TPS too, and if I still have the problem then I'm really not sure what I'll do next.