I had the same codes and I'm still working on it. I cleared them and only the P0171 comes back. I read that one common solution is to clean the MAF sensor. I did that and the P0171 came back. Next I'll look for vacuume leaks and replace the PCV.
I just changed an alternator out in my 2002 gti 1.8t. It was running fine but then I just took it on a long drive through jersey. When I got back my check engine light was on. I brought it to autozone and got the codes p0171 and p0507.
I immediately changed my spark plugs because I knew they were terribly old. After that the check engine light remained on. I did some reading and I found that it can be a leak in a hose, the pcv valve is plugged, or o2 sensor.
Online I read that you can pull the dipstick and if it sounds like pressure is released when you do, the pcv valve is bad. I went and tried this and this is definitely the case. I feel there is pressure on the dipstick and when I pull out the engine idle lessens and then comes back up to speed.
What is odd however is that my idling rpm seems fine, it's not jumping around or anything. I simple just have a CEL and I need to get the car inspected.
The P0507 is a code that idle is higher than expected . Now this can fool you. Your idle may appear fine, but what is happening is that the Throttle Body is having to close farther than programmed specifications to try and correct for the extra air caused by a vacuum leak. That throws the P0507 code.
Last edited by Chickenman35; 10-16-2012 at 11:00 AM.
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