What will cause a rough idle...

and after warm it idles at 500 or so, to what ive heard on these forums thats too low, so what do i need to do to fix that?

 

Try cleaning your AIC. It controls idle and can get alot of carbon on it. Do a search, im sure that there are a bunch of posts for this.

 

Check your EGR valve also, if that's stuck open you're car will idle rought.

 

also, if its idling that low, there might be a vacum leak...

 

well with an A4 ur supposed to idle at 550 rpm when warm. my tach reads 800 while my computer see's 550. so maybe ur tach is off a bit, but for the rough idle, i dunno, do those suggestions above

 

when warm my car does idle at about 550, but on occasion when cold it idles at about 900 or 1k, i have to make much more use of the brakes at lights and such, otherwise my car feels like its going to launch. What could cause this?

sorry to hijack your thread