Hey, all,
I'm rather new to this site so bear with me. I've had problems with my 2000 a4 1.8t since I bought it in 2006. Back then I would get codes to flash up and then they would dissappear again almost as soon as they came. About after a month or so the check engine light came on and stayed on, so I bought an engine reader (one for vw/audi only). The first codes I got were 17536 Long term fuel trim too lean. I put in some fuel additive cleaner and the problem went away for a while. A few months later codes came back along with a hardly noticeable power loss. By the time I got around to fixing it I had six codes, and forum hopping and asking friends all pointed to a faulty O2 sensor. I replaced the sensor and sea foamed my engine, but after clearing codes I retained two: 16795 & 17536.

16795 or P0411
Sec.Air Inj.Sys. Incorrect Flow Detected

17536 or P1128
Long Term Fuel Trim mult.,Bank1 System too Lean

All the forums I've seen point to either a faulty MAF or maybe some Vacuum hose leaks, but I don't know what to do- also my repair manual doesn't tell me how to find my MAF sensor- it tells me how to find one for a six cylinder, I think. So help on that would be appreciated as well...

 

Also, I forgot to mention that my turbo has never worked right, and I'm not sure but someone mentioned that the PCM shuts down the turbo function whenever it has codes active- is that true? By not working right I mean that it only shoots rarely and when rpm's are above 5000 (which I never really run it at anyways, I only noticed it when going through the sea-foam procedures)

Also, feel free to ask about any history, I would put it all here, but I'm trying to avoid writing a book.

 

it is possible for your car to go into limp mode if your running lean to avoid damage, to me it sounds like ur 1st o2 sensor is bad and one injecter is clogged. (this is just looking at the code, i have no basis for my opinion.)

 

Long term fuel trim too lean is most likely just a vacuum leak. It's common that the braided Audi/VW vacuum lines get brittle and crack open every few years. Just buy 8-10 ft of vac hose at an auto parts store and replace the line from you DV to underneath the intake manifold (that's the hardest one to reach/replace), the short one from the intake manifold to the FPR (easy), and the others. Check the bigger lines for leaks after that. You should have improved throttle response. No more rough idle, and the code shouldn't come back after you clear it. Even if you find a broken hose, don't stop there. Check and replace them all. It shouldn't take a newbie any more than 1 hour to do it. There is also a vac line diagram on a sticker under the hood, so you should be able to identify all the hoses. Do that and check back when it's fixed.

 

That acutally sounds like it could be it, especially considering that I replaced the pre-cat O2 sensor already. I did notice the vacuum lines did not look in the best of shape, and it could explain the nature of the problem coming and going. I'll try that and tell you what changes. Thanks, Bogie.

 

Replacing the vacuum line caused one code to go away, so it probably needed to be done, but what should I do about the remaining code?
16795 or P0411
Sec.Air Inj.Sys. Incorrect Flow Detected

any tips or redirections?

 

New update: after a week or so both codes came back, so it wasn't the vacuum hose after all. If anyone has any new ideas I'm all ears.

I heard something on another forum about a multi-switch or something. Could that be my problem?

 

I've got the same issue though I cleared the DTC and only 17536 keeps coming back. I'll let you know if I find anything out.

 

Can you hear the secondary air pump run when you start the car cold?

 

I don't mean to bring up an old post, but here goes: i just tried to fix the line from the DV to under the intake, since it was not connected and throwing the lean code, but i couldn't get in there to put a clamp on it under the manifold. any suggestions? will moving the oil dipstick over slightly to get in there better ruin anything?