Mystery problem

[brettle0]

Hey guys,
So my stage 2+ 2007 A4 auto has started dying any time I turn it on. In park idling, the rpm's fluctuate constantly between 600-1400. Any time I put it into gear, it immediately sputters till it dies. I thought it was the MAF, and so I replaced it with a refurbished one from O'Reilly, but when I installed the new one, it had the exact same symptoms. When I unplug the MAF from the harness, the car drives, but it's like it's in limp mode and it doesn't seem like any boost is making it back to my engine. It's not throwing any codes besides a P0100 that I assume is from me unplugging the MAF. Any help would be appreciated, thanks in advance!


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[Audibot]

Sounds like a have a vacuum leak in the system somewhere. When the car is cool, I'd start it and spray it with some soapy water to see if you can find the leak. If it bogs down, you are in the right vicinity.

[brettle0]

I was thinking that as well, but I'm confused. If it was a huge vacuum leak, wouldn't it be present with the MAF unplugged? It should die with or without the sensor plugged in, right?


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[Audibot]

Maybe if it's trying to adjust too much with the MAF in, but not on whatever the one set without the MAF. W.r.t. when you drive it and it has no power, double-check the boost coupler on the turbo to the intercooler. I've had that come off before and the car basically limped along.

Another few areas to check are the N80 valve, PCV and throttle body. All of these seem to be able to cause it. I'd start with the N80 in case, because it's stupid cheap.

[brettle0]

Audibot you got me on the right path. My front mount intercooler hose popped off, but still looked like it was attached. You're the real MVP man.


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[Audibot]

Good to hear it! Experience is the best teacher, they say.

[B5A4coastie]

My B5A4 had a rip in the T-coupling at the DV, it took me 2 weeks to find the boost leak because of how well it sealed at idle.... Glad you found your issue.

[Charles.waite]

With the MAF unplugged the ECU reverts to failsafe mode and runs on premapped settings. Its possible your intake piping slipped off so you have a huge intake leak. When air is being sucked in after the MAF the ECU freaks out and makes all sorts of running issues. I would check all your intake pipes for leaks and make sure the clamps are snug. Also check you Turbo inlet hose for leaks.

[Word602]

Audibot you got me on the right path. My front mount intercooler hose popped off, but still looked like it was attached. You're the real MVP man.


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Where is was this located? I got the same problem. Driving without maf right now. Im on my 3rd maf in last 3 days. They all do the same thing. My voltage seems to check out find though. Could you feel air in that area?

[brettle0]

I popped an intercooler hose so none of the air from the turbo was getting into my engine. That being said, I have a front-mount intercooler. If you've been through 3 mafs it's probably not that. I would check your intercooler hoses, Intake pipes, and turbo inlet hose.


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[Audibot]

I popped an intercooler hose so none of the air from the turbo was getting into my engine. That being said, I have a front-mount intercooler. If you've been through 3 mafs it's probably not that. I would check your intercooler hoses, Intake pipes, and turbo inlet hose.


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Like brettle0, I had a FMIC and popped off the hose. Called up my shop in a panic and he set me straight. Had it happen again and knew what the fix was immediately.

I would also say the MAF isn't your problem; you likely have a vacuum leak or PCV issue somewhere. Intake leaks past the MAF will cause all sorts of problem b/c the computer expects x g/s of air and you're giving it y g/s.