2007 MKV GTI 2.0T IDLING TOO RICH

[Whiterabbitwhiterabbit]

Hi all,
My gti is idling high at 2100-2500rpms (I know!) then down to 1000-1200 then back and forth. I’ve read that it could be the pcv valve, a coil pack, or a vacuum leak somewhere. It doesn’t miss when it’s in gear and I’m not losing a significant amount of power
It is a stock 2007 gti Fahrenheit model with the exceptions of the downflow exhaust and cold air intake. I run 93 octane and lucas fuel treatment every tank and liqui moly leichtlauf 5w-40 every 5,000 mi. The vehicle has 165K and the motor replaced at
115K.

 

[3carmonte]

A tech-support once asked me as I called from a customers site begging for his help, "what's the last thing you did?" On topic, the last thing I did before I introduced a vacuum leak and had some of the symptom you are describing (but not to the extent you are experiencing...) was I replaced my cam follower and cracked one of the custom formed plastic tubes in the brake vacuum booster system. They, like all plastic; get brittle with age. So, what's the last thing you did before you had this symptom? Start there.
Are we talking a MKV-fsi power plant here?

 

[GTI's]

Hi all,
My gti is idling high at 2100-2500rpms (I know!) then down to 1000-1200 then back and forth. I’ve read that it could be the pcv valve, a coil pack, or a vacuum leak somewhere. It doesn’t miss when it’s in gear and I’m not losing a significant amount of power
It is a stock 2007 gti Fahrenheit model with the exceptions of the downflow exhaust and cold air intake. I run 93 octane and lucas fuel treatment every tank and liqui moly leichtlauf 5w-40 every 5,000 mi. The vehicle has 165K and the motor replaced at
115K.

Welcome to the forums.

I see you have a check engine light and also bulb out icon. Have you scanned this car for trouble codes yet. If possible find someone with Vcds and have an Auto Scan done.

 

[Whiterabbitwhiterabbit]

I did scan! Thank you for the responses. Going back to the last thing I did — adding too much coolant, I assumed was causing the engine to overheat itself on purpose to expel extra fluid but alas, the scanner takes the prize. Codes ( beginning with the letter P -0 ) 171 139 507 and, later 300-304 (misfires in each cylinder) came up. After replacing coil packs, spark plugs, and fuel filter a multitude of issues are resolved however I believe the culprit remains the two modifications made by the previous owner which are down flow of the exhaust and the cold air intake. My cousin, Joshua (a mustang fanatic and electrical genius) assisted in getting to the core of the problem and today I will be replacing the upstream and downstream O2 sensors.