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Tiny idle surging only when car has been fully warmed in P or N?

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BudgetPhoenix

Autocross Champion
Recent phenomena with my car. My 09 TSI dsg will start surging idle from 750-850rpm as soon as it hits 190F on the temp gauge, anything before and its totally fine, and when in any drive gear it will have no surging. Zero codes relating to it, ive tried checking everything, new PCV, smoke test, vacuum lines, intake, intercooler piping, reflashed stage 2, disconnecting maf makes no difference, cleaned both maf and map sensors. If I clear codes while its idling it seems to clear it up until it relearn and starts doing the same thing. My boost gauge will fluctuate from 20-21hg when its doing this, its like a rythmic surge you can hear and feel through the seat. The rpm gauge doesn't really move at all like when I had a bad PCV and it started misfiring and shaking revving up to 1500rpm by itself. Anyone had any issue like this before? Driving me nuts
 
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nickp1

Ready to race!
My 2014 with 48K on it does the same thing. I think it is from carbon build up but I am no expert. Although i am not sure mine is a 100RPM range but smaller. The needle bounces though as described when warm.
 
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BudgetPhoenix

Autocross Champion
I pulled off my map and cleaned it out real good again with some electric cleaner. Warmed it up in my garage and it seems to have leveled out the idle. I need to go drive it hard though tomorrow it seems to like to do it after driving it. Also I was getting a soft p0507 code now too. Seems like it should be a small vacuum leak with that code but I cant find it. Ill report back


edit* I too thought it might be carbon buildup its a possibility. I know it was last done 30-40k miles ago with previous owner according to dealer
 
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nickp1

Ready to race!
My car seems to have stopped doing this... Maybe when it gets cold out it will start doing it again.
 
zrickety

zrickety

The Fixer
Sounds like a vacuum leak, maybe one of the rubber hoses.
 
B

BudgetPhoenix

Autocross Champion
I figured it out, it was the PCV. Confused me because it was new but there must have been a tiny hairline crack or the gasket wasnt sealing properly that it caused a leak but only a tiny one
 
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