I've been having this problem for quite a while.

I have a 2001 A4 1.8TQM 80k miles on the clock with a GIAC chip,borla exhaust, and evoms dv.

I used to spike at 21psi and hold 19-20psi. It now will only spike to 15psi and will drop down to around 10psi. It will surge and hiccup when I'm on half throttle. It seems like the car is trying to go and smoothly hit boost and then it just stops suddenly. It seems to be happening around 2500-3000 rpms.

I have no codes and am not in limp mode.

I've done the following:

Ngkbkr6e plugs gapped to .028
new maf sensor
new n75 valve
pressure tested twice not a single leak anywhere
software reflash


I checked the turbo for shaft play and it doesn't seem like there is any noticeable problem. This is really frustrating as it has been going on for a few months now. Not even shops can figure it out.

My only guess is a bad wastegate or bad map sensor. When I vag com'd the car the map sensor altitude stayed at -4.7 and didn't change while driving...I cleaned it last night with rubbing alcohol and there still was no difference.


What do you think guys? Anybody else out here with this problem? Any feedback would be great!

Just tried taking off the vac line on the wastegate...the car boosted up to 21psi again and felt great but didn't feel as powerful like it used to...also i took out the o2 sensor and it was covered in white.

I'm leaning towards a bad wastegate????

 

except i knew where to look because mine rattled under boost, something inside had shattered.

stupid question: have you ruled out the dv?

 

collection of how the turbo system works in the a4 and how to diagnose and pinpoint certain problems and running conditions that could come up

 

pertainin to the B5 A4 and common problems that you will see if you own one.? I think that sounds like a great idea... get on that Stephan...

 

that contains "all" the turbo problems

 

What kind of Gas mileage do you get when your O2 needs replacing?

 

less then when it does not need replacing