So I have a 98 a4 1.8t. .63 trim t3/t4 turbo, 10psi. Stock ecu at the moment.

The car runs okay when cold, once it warms up it hunts for idle, sputters and bogs when I try to accelerate, and stalls sometimes. When it does this my wideband reads 10:1 afr and on vagcom under throttle position it shows "enrich" even when the car is at idle. I'm pretty sure it's dumping fuel for no reason...

Scanned with vagcom and found code p0121. Throttle body signal erratic.

Checked wiring, cleaned throttle body, performed tba with vag-com. Same problem, same code.

Replaced throttle body and did the tba, still the same thing.

Checked throttle body wires, replaced ecu, performed another tba. No help, but after the ecu change I got codes p0121 and p1555

However, if I unplug the maf, the car will run and drive, I just can't get into boost past 7psi or it will start to run lean. I did replace the maf to rule that out and it still is doing the same thing.


Other parts I have replaced are: plugs, coil packs, ecu, maf, throttle body, icm, upstream 02 sensor.... I am completely stumped and out of ideas. Someone please help me.

 

If it runs alright with the MAF unplugged, then my guess is either air leak, or simply that the stock tune is unable to cope with your turbo. Or both.

 

It still runs crummy with the maf unplugged, but driveable.
I wouldn't think its the turbo because it had been running fine before, and it does it when im not in boost at all...

by air leak you mean a boost leak?

it also only acts up at operating temp

 

I do mean boost leak, but when not boosting a boost leak will be a vacuum leak. In any case a leak can cause and engine to run poorly, whether in boost or not.

With the MAF unplugged, I would suggest clearing fault codes to reset the ECU, then drive it. It's possible this will make a difference, and will help with our Internet diagnosis.

 

Okay I cleared codes and checked visual leaks in vac lines and ic piping, everything seems fine. also pulled the vac line off the fpr to make sure there wasn't any gas in it and it looked good so I assume the fpr is good.

drove and got code p0121 and p1555 again. drove well for about a mile, then started to stumble, then after another half a mile or so it wouldnt even let me accelerate at all, it just sputtered. when I stopped and let it idle, the idle was a little high(1k) and my wideband stayed on 10:1 afr. Shut of and re started the car immediately, and the idle and afr were fine.... This is aggrivating lol.

Going to check my pcv valve next, although Im not sure if that would cause these issues.

 

With the maf unplugged it drives better, still hesitates a little but doesn't buck or stumble. Does run a little lean when in boost which is to expect. And the p0121 actually didn't show back up this time with the maf unplugged. It only shows the throttle body code when the maf is plugged in.

 

Update: made a boost leak tester, found a torn coupler and vac line elbow. Fixed both and test drove, car is running a little better but still stumbles and hesitates some. But did not stall.

Also is throwing a p0103 maf high input code, but the maf is new. Hasn't thrown a throttle body cod again

 

did you reset the ecu after the fix? not sure it'll help but it's worth a try

 

I cleared the codes but that's all I did. Is there something else I should do to reset the ecu?

 

no that does it