ok so i just replaced my MAF that was throwing a CEL.. I went ahead and erased the obd2 code with my scanner.
As i was replacing the MAF, i noticed the in-line check valve was busted..
see image:



So I took the car for a drive, and now as soon as the turbo starts to spool, it seems to "pulse" in and out of boost, enough to feel like a bad bad misfire.
I drove around the block a few times very light-footed and haven't pulled a new CEL.

Should I assume that now that the car is out of "limp mode", that the extra boost is being messed up by this valve?

Or should i look elsewhere to resolve this problem?


btw..I have GIAC 91-93octane...if that helps.

 

Haha.. Same EXACT thing happend to my check valve at the same location. I didnt have any noticeable running issues when my valve was rotted out like that. I happend to find it during a boost leak test, fixed it, and didnt notice any improvements afterwards. If you just replaced your maf, give it some time. When I replaced my maf, it seemed like it took it a day or 2 for boostlevels to be moreconsistant. What are/were your fault codes?

 

I have the code written down at home... I think it was p0174.... the description was something involving air/fuel metering...

but you think the crazy boost issue will go away in time?
because i'm kinda afraid to drive it..

 

You should be ok, just replace that check valve first and see what happens. If you have a problem after replacing that known bad part then we will diagnose whats going on.

 

The check valve it to the EVAP system and will cause a large vacuum leak. It rubs against the metal clip back there. Not uncommon problem on the A4.