I have a 2005 2.0t Quattro A4 with 113k miles. I've noticed this week that the idle RPM will jump to almost 2k at times and is very unstable. It never dips below 900 but will go up and down from 900 - 2k.

I changed the oil a day ago and Last night i changed the spark plugs - didn't resolve the issue. I checked the airfilter (K&N) and it's clean. I don't hear any air leaks anywhere.

Mods done to my car are as follows: APR 91 Program w/ Test pipe program, Test Pipe, Forge DV, K&N Drop in filter.

I'm not sure where or what i should check next. Also i'm scheduled to do my timing belt/water pump in a week. Could my timing belt be the issue?

Any help is greatly appreciated.

 

I just started having the same issue yesterday on my '05 2.0t (no mods). My car only has 58K on it. My check engine light has been on for a few months...it's coming back as a cooling system issue. My independent shop seems to think I need a new thermostat. This idle issue has only been happening since yesterday.
I'd love to know what people have done to remedy the problem as I'm supposed to take my car in to get the new thermostat next week, and it would be great to fix this issue at the same time.

 

My issue was the PCV. One of the first to go when chipped even on stock boost. BSH makes a great one.