I know this was on my truck, but it's the same as the RS's so here it is.....

I had been getting an increasingly higher idle for a couple of weeks, plus it would crank longer before starting, So decided to check it out. I was hoping the TB wasn't worn out...

I sprayed carb cleaner around using the red straw on the can, and the motor really bogged down when I sprayed near the base gasket of the Throttle-Body. So I removed it for inspection.
Somehow a large piece of the gasket was missing, aprox 1" long.
I scraped down the mounting surfaces and installed a new gasket and it idled down perfectly.

 

Thats good advice---that happeded to me over a year ago.

It got way better for me but it does idle faster then new cars still--and I have to "kick it down" every once in awhile.

 

I remember when that started happening during the summer, car would go up to 1700 rpm idling, always had to kick it down...I don't know why but I must have been in a hurry and the car was idling around 1700 when I put it in reverse to pull out...was a quick jolt