sooo i had rb headers put on and an exhaust. recently i have found that my car is idling way low, like 5-700. my car starts shakin like its gonna die i tried turnin it up with the little screw dealie but did nothing. when i first start it up it revs to 3 then drops to 15 then once put into gear goes down to 5. then later today check engine light came on. im not sure where to start never had this problem please let me know if you have any ideas thanks

 

When you start it up the engine will rev to 3000 as part of the accelerated warm up process. You can cancel that by putting the car into gear, or if you have an S5(not sure if this works on s4's too) blip the throttle.

It sounds as if your problem is your TPS(throttle position sensor). My car does the same thing, only when its warmed up and driven for a while, next time I start it up it will try to idle at 100-250rpm and my check engine light comes on. Just turning that screw you mentioned wont do anything unless you have a sensor that tells you when to stop turning it. Not sure what that is, i just used a friends. Idling at 500-700 isnt bad though, as long as its constant. Normal idle should be withing that range any ways.

 

did u try warming it up b4 u drive? or it can be a leak

 

well i always let my car warm up, until it does the 10 seconds 3k then after that drops to 1500 and stays there for as long as it wants until i throw it in gear than it drops to 5-700. the tps sensor was just replaced so i dont see why that would be a problem..

 

Could be the BAC.