Don’t post here as much as I used to, mostly because I don’t drive my car as much, but still like to troll and see who’s doing what with their rides and to read allroadinvail’s funny ass responses to people’s posts. Anyway, I have an ’02 B6 A4 1.8TQM with an APR tune and bigger injectors. I haven’t had a lot of issues with the car but when I gave it to my buddy to borrow and wrench on a few weeks ago it seems like it came away with the same problem it had when i gave it to him and my pocket feeling a bit lighter.
The reason I had given it to my friend was he has lots of experience working on VAG cars and my car kept going back and forth between full boost and limp mode, all in the same journey. For instance, I’ll be driving up I-70 westbound up the winding hill from Golden to Floyd Hill and the car would be in full boost (around 15 PSI). If I let off the accelerator slightly when coasting or maintaining speed in traffic and then gave it some more gas it would only give me 5-7 PSI. This would happen, and still does, driving the whole way up to the mountains to go skiing. I was told it was throwing codes for a Front O2 sensor and I also had a boost leak, so I bought some parts and let him go to town fixing the boost leak, among other small maintenance items. All said, I spent around $900 just on parts.
I got the car back and within a day of driving it I noticed the same issue again. I told him what was going on and he was stumped, unsure of what the issue could be. I did some digging on Audizine and a few other sites and came up with what I *think* it could be:
1. Faulty N75 Valve – from what I’ve read it doesn’t throw a CEL, as the only one I have now is for the SAI Pump, and since it controls the wastegate would make the turbo think it’s boosting too high and kick it into limp mode as a safe guard
2. Boost leak – just had my guy go through the whole car and fix all potential issues so I doubt it’s this, but stranger things have happened
3. Diverter Valve – Broken DV means all charged air goes directly to atmosphere which means no power. Wouldn’t make sense though as my car can still produce full boost but is intermittent
4. Other – I have no f’ing idea what it could be. Could I just leave the car as is and keep going back and forth from full boost to limp? Or do I stand the chance of making things worse?
I’m hoping some of you may have heard of something like this before and can give me some suggestions. I don’t own a VCDS cable so am unable to run any data logs on any of the blocks. Kind of at a loss as to what it could be at this point and hoping someone can help a guy out.
Look forward to hearing all suggestions and at least one comical post from allroadinvail (I still owe you Bud’s for the center caps that are still presumably in Jace’s garage).