My 2001 1.8t loses boost after 10 minutes of driving but after I restart it is fine again for another approx. 10 minutes. I have since put a new cat, new blow off valve and ran codes. No codes show. Boost is great the first few times I really spool it up but then it just goes away. I am pulling my hair out over this. Please help!

 

check your exhaust manifold it may of come loose or it may have a crack init or you don't have the bolts that hold the turbo to the cat tight enough

 

I hope that was a diverter valve, not a blow-off.

 

with all that stuff you replaced, im sure a boost gauge was installed too right? what are your boost numbers? how much boost are you loosing? do you actually know you are loosing boost?

if you were going into limp mode (5psi) for whatever reason, there would be atleast one code stored. if there arent any codes it could be a leak somewhere. but with no boost gauge youl never know.

 

For many years I have been a Service Advisor for Porsche, Audi, Mercedes-Benz and BMW. I have a wide spectrum of knowledge on all German vehicles. I changed the oversized alternator on my car in 1 hour without even removing the radiator when they said it would take 5 hours with removal. I've never run into this problem and obviously niether has my local Audi store. There is no exhaust leak that I can hear and no I don't have a gauge on it. This thing is a snail but even more of a snail when the turbo is not working. The basic story is it runs perfect and has boost on cold start. You can hear the whistle from the turbocharger every time you take off. After I leave the house and get on the highway opening it up a bit it starts to get weak when passing someone. When I come to a stop and take off again.... No boost. You hear nothing from the turbocharger and it feels like i'm running on straight motor. I was just wondering if anyone else has run into this sort of problem.

 

You should try changing the oil pan on these things. Not Fun!

 

yea you get to drop the subframe. er atleast half of it.

im not questioning your experience, but you need a boost gauge to quantify any change in performance. stock boost is 8psi, limp mode is 5psi. the difference between limp mode and stock boost pressure is almost impossible to tell to a certaintty. also the difference between zero boost (from a leak) and 5psi is just as hard to tell without some sort of gauge.

you dont know if you are in limp mode or if you have a leak and are hitting 3psi. also you will be able to look at how much vacuum you are pulling and instantly have a pretty good idea if there is a leak or not. have you scanned for codes yet? that would be the first thing i would do. leaks dont normally throw codes unless they are enormous.

since you said it is fine after a hot restart im going to guess its a sensor throwing you into limp mode. if you have 100+k miles on your knock sensors they might be on the way out and will cause that. also look at the MAF or primary O2 sensor.

 

Well there are definitely no codes and the gauge idea makes a lot of sense. The only way a leak would make a difference is if it gets bigger as the engine gets warmer but i will try it anyway. No sensor codes are showing but the knock sensor will not show a code even if it goes bad. I may try that too. I may try 2 other things, the wastegate and the valve under the intake. Ive been told those are both troublesome