serached but didnt seem to find "my" problem...
every morning or when i start my car after it has been sitting for a while the rpm's keep going from 500rpm's to 1,000 rpm's.. the car kinda shakes a little this goes on till the car is warmed up or till i give it some gas.. the wierd thing is that this only happens when the heater is on or the a/c...

 

you can check for vaccum leaks, but when the heat or vents are set to defrost, the ac is on or you have the rear window defrost on it does this. how is the idle after the car is warmed up and the ac is off, vents are set to floor/dash?

 

Um, an 05 VIII? Isn't it still under warranty?

S.

 

Oh, wait, you modified it... They probably won't warranty it - unless you remove the mods!

S.

 

Sounds like you may be experiencing an issue with one of your O2 sensors faulting.

 

I doubt it's an O2 sensor since the ECU would run open-loop before the engine warms up (and thus pretty much ignore the O2 sensor since it takes a little while for it to reach operating temperature).

I think the best bet would be to check for a vacuum leak first. The A/C doesn't really affect the engine except as an additional load, which could potentially aggravate a problem. The heater (without A/C) is a bit puzzling though. That's pretty much just a fan (blowing through a water-to-air heat exchanger). It does present an additional electrical load on the system, but I wouldn't think it would affect things so greatly - unless maybe you have a faulty ground somewhere. That's something else to check.

Thanks, and good luck!

S.

 

His mod list answers the question!