I have a 99.5 a4 1.8t and have done some searching on here for some time for my problem, but to no avail... I am experiencing a low power problem. Basically my car feels like it doesn't have the ummphh that it did when I first bought it. I replaced the DV today with a Forge 006 and it still felt underpowered. A couple of days ago my car boosted and I could hear the turbo spool up and power felt like it did when I first bought it, but then two minutes later after i switched through a gear it went away, back to a low power feel. I just recently replaced my cat with a test pipe and did the non fouler mod as well, but it still through a CEL. However, even though the CEL was on the 2 min boost spike still happend and the car actually hit fuel cut in 5th gear. Do you think it might be the N75 or what? Sorry for the long description but I felt i should explain it all so you guys could understand what's going on.

 

you should check for codeds, and see if your in limp mode

 

deffinately sounds like limp mode.. Get some codes and we can help. Im guessing you are chipped? Also a guess, but you might have overboosted and went lean which put you in limp mode and gave you a cel. That happened to me (would go into limp mode after doing wot at high rpm's) just recently and it turned out my ects was bad and making me run lean. Since i replaced it theres no more limp mode with wot high rpm's and the car runs a lot better in general. Again, just a guess, cuz i had the same symptoms as you.

 

I don't know of anyone that has a VAG com, but i did go to auto zone and did a generic check, it did pull up a code for the 02 sensor below threshold and after that I cleared it... It came back on a 100 miles later, then a short time after that is when I was experiencing the 2 min boost issue. It's really fustrating cause the car felt alive again when it happend.

 

Might want to replace the 02 sensor then, if that code keeps coming back. Also check other things that would cause an 02 sensor to fail like things that make you run rich like a boost leak/maf/plugs/not using proper octane gas etc. It might just be dead though, they should last 90-100k miles if everything else is working right. So just because you get an 02 sensor code doesnt mean that the 02 sensor is all thats wrong. You might replace it, and it could die again 5,000 miles later if there is an underlying cause. Replace the 02 sensor regardless If its the original 02 sensor on a 7 year old car with near or over 100k miles, and everything else checks out, its probably just time for a new 02 sensor. www.oxygensensors.com has the best prices on 02 sensors that ive seen btw.

 

ok when you recommend a new o2 sensor which one are you referring to? The front or rear? I am assuming the rear, but do you also think that since I used two short non-foulers for the rear o2 sensor, that going to a long short setup my fix the "below threshold" code?

Oh and also I am not chipped and I don't understand how replacing the ECTS would effect my performance since it was acting like a low power car prior to it boosting well.. That's the only reason how I really knew my car was underpowered by the dramatic difference in how well the car spooled and pulled. Sorry for all the questions guys.. I am searching too!

 

Ok I just got back from autozone to clear my codes, it did pull up a ECTS code but since i cleared it I would assume that it also would make the ECU go out of limp mode.. But it didn't do a thing, performance was the same but throttle response was a little better but i think that would have to do with the Forge DV. On my way back I heard a jetta 1.8t drive by and a convertable 1.8t beetle drive by and I could hear both of the turbos spool like mine did as I described earlier. I am starting to think I am a case where I have multiple things wrong at one time to cause this issue.

 

Change your ects for sure. A bad ects can throw an 02 sensor code as well. A bad 02 sensor, regardless of wether codes or a cel is present or not will give you poor performance.. So will a bad ects , but start with the ects as it is a fraction of the cost of an 02 sensor. If after that you still feel something is lacking or are getting an 02 sensor code/cel-change the 02 sensor. If your car has 90k + miles, it would be wise to change it anyway. Usually the 02 sensor that affects your performance is the one closest to the manifold. Your car is still gunna be slow though, its got 150hp! what do you expect?? Get chipped!!!!!! The ects plays a big part in your engines performance, even though by the name of it you wouldnt think so.

 

Thanks man for your help, I'll keep you posted as I fix these diagnosed problems.

 

I'm all for changing your ECT sensor. My car was running like poo for a month b/c I had no time to change it. I used my vag to clear the code but it would come back in a couple days. I noticed the decline of performance during the time, too. It ran great at the first start it up then got worse and worse until the CEL finally came back. Since I've changed the ECTS, I remember why I bought the car, IT'S FUN TO DRIVE!!!

Also, have you considered the fuel filter? Just a thought but I'm not a mechanic.

GL.