ok so i have an o1 a4 1.8 quattro engine code awm. i have a borla exhaust and a test pipe on the car. for a while its been running great boosting to about 9 ish psi but recently out of the blue i guess it went into limp mode. i replaced both o2 sensors and it ran normal for a day. the next day i go to drive it on the highway about 20 mins into driving it just boosts up to 5 psi. all my vacuum lines are hooked up ive been all over this motor. any ideas? maybe if id throw my cat back on? i dont know any ideas suggestions? thanks alot

 

Even if you have no CEL, scan for codes. You may have a latent code that isn't tripping a light but can clue you in. A possibility - check the wastegate actuator. If there's something out of whack with it, it will definitely affect your boost.

 

Check all the pressurized induction pipes too, from the turbo, through the intercooler, up to the throttle body - a leak in the charge pipe will kill the boost too.

 

thanks i forgot to mention that if i disconect the battery and wait like 15 mins and reconect it itll run at full boost for like 10 mins driving down the road and then turn into a turd again

 

Have you replace the vacuum hoses? They might be hooked up but have holes. Same thing happened to me, also clean your maf with crc? maf cleaner. Then reset your battery.

 

yup i have brand new sillacon vacuum line and a new maf i pretty much hate my life right now over this car

 

If we chill sunday ill take a look. Well have a problems look cause my cluster just freaked on me and my engine just started making noises so well have alittle prolem discussion haha

 

get it scanned, its obviously electrical with that one sympton of unhooking the battery and reconnecting it again making it run better.
if your buddy kito is swinging by, why not swap N75 valves. or even try running your DV straight from the manifold bypassing the n249 under the intake manifold (first one closer to the rad) and plug it.

 

well removing the battery would reset any soft-limp mode that you were in. first step is to get the car scanned as already mentioned.

ive seen this happen when one of the knock sensors start to go and throws an incorrect reading. a knock sensor is essentially a microphone that has a bedding material surrounding it. that bedding material breaks down after 12 years of heat cycling. if none of the above suggestions work, that is another idea to look at.

 

thanks for all your help!