I have a 99.5 A4 Avant 1.8t Quattro. I have an APR stage 1 chip, cold air intake, evo bypass valve and about 72,000 mi on the car. I seem to have developed a problem.When I accelerate hard (3/4 throttle or greater and above 2000 rpm) the car begins to shutter and buck. If you don'taccelerate hard there are no issues. Also if I turn my chip off it still happens, but not as bad (I think it has to do with boost over 6 psi or so).

The first thing I did was wash and re-oiled my air filter which didn't help. I also added some octane booster to my tank but that hasn't appeared to help either. Do you think it could be a boost leak? My check engine light has not come on and nothing else seems out of the ordinary. Over the last couple of years I have not driven my car much and generally only put on about 3,000 mi a year. Could it be dirty injectors?

Any insight to my problem would be helpful. Thank you for your help.

 

maybe a boost leak or you might need to rebuild that DV also could be a bad N75 valve

 

2nd, that check for a boost leak, & leaking DV.

 

One more question. I have also noticed an increase in oil in the intake tubes. My diverter valve has an oily residue on it and so do some of the intake pipes. I realize some oil on the inside is normal, but what if the outside of the intake plumbing starts showing signs of oil on them? Could a boost leak cause an excessive amount of oil? I don't notice a change in my oil level between oil changes, but it worries me. Thanks again for your help and any insight you can give.

 

The only way oil can get on the out side if from a oil leak. It might be from a loose hose, torn TBB, or the wonderful valve cover gaskets. With out seeing the car, I can't help much.
If you over fill the oil, it will end up in the intake pipes.

 

Thank you again for your response. I have most of the intake tubes apart and the oil appears to be coming from the crankcase breather pipe. When I removed the crankcase breather pressure reulating value there was a small amount of oil that physically ran out of it. There is a chance that I could have over filled the oil during an oil change, but not by more than half a quart. Would the oil in the intake tubes come from just a half quart too much?

Second question: How would I check to see if the waste gate bypass regulator valve (N75) was bad? If this part was bad, what kind of behavior could I expect while driving or accelerating? Is there anything that I should look into that might help youdiagnos my problem?

Thanks again......hopefully I can get these items fixed soon.

 

Purchase a Bentley CD repair manual.

Yes, to much oil will find it's way out of the engine, even with a perfect oil level there will always be some oil blowing around. You might want to change the one way valve.

If the N75 is bad, you will get a code. If it's on it's way out, you will still get a code & weird boost, and yes maybe some lag.
To test you check the internal resistance. I believe it should be around 28 ohms. If it's not close to that, it's bad.

 

It may be the plugs if you havent uprate to higher temp plugs or just ran the engine hard when it was still cold. i was having the same problem with my car until i replaced the plugs, the old ones had alot of glazing on them which caused the hesitation.

 

I put some Denzo Iridums in about 6,000 mi ago and have not had any issues until recently. Do you think it could be a coil pack? I looked through my service records and it doesn't look like they have ever been changed. Any other ideas? So far all of the vacum lines and intake lines appear to be fine, no breaks that I can find. Also still no CEL light at all.

 

New news. I pulled the plugs tonight and they look good. The gap is a little large per my Bentley Manual (recommended gap for AEB engine .70 to .90) The gap on my Denzo's was 1.01 mm. Could this be the issue? If I do change out the plugs what would you suggest?I also rebuilt my diverter valve and that did not appear to help.
However in another test drive tonight I noticed that once the boost comes on, at more than 3/4 throttle, I only have the lurching issues from about 2,000 rpm through 5,000 rpm, however once your above 5,000 rpm there is no lurching or loss of power.
I am still trying to find someone to scan my car for me and hopefully that will shed some light on my issues (still no CEL though). Any ideas again are appreciated. Thanks!