I have a 2000 S4, with the 2.7t, with tiptronic, also has a stage 1 tune from VAST (before they got dismantled) with rear O2's delete, SAI delete, and EGT delete. It has about 168k on the clock. I'm getting tired of always fixing this thing... my wallet is really hurting as well.

So this problem has been going on for a couple days now, and I thought I had it fixed. I need some help trying to figure out what it might really be.

I was driving home wednesday, and my car started acting funny. Starting bucking a little bit, and the rpms would randomly drop about 6-800 rpms. It didn't happen a lot, but probably 5 or 6 times. Got it home, let it sit all night, and didn't really do anything with it. I drove it to work thursday morning just fine, no problem at all. Thursday afternoon I'm driving home, and it starts doing it again, but it gets to a point I can't drive anymore. I was about half way home and it went into limp mode and the EPC and check engine light came on. I pulled into a parking lot, checked the code, which was p1633 (link here to wiki rosstech for code. I called the local vw/audi specialist shop and talked to one of the techs there for a good bit. We came down to a determination that it was either the pedal, the ecu, or the wiring in between the two. So I set out on the pedal first. I pulled it out while I was sitting in the parking lot, took it apart, wiped down the inside a little bit, and put it all back together. After that was done, I started the car up and drove home with no problems whatsoever. So I figured it was the pedal, and decided I'll get one at a pull and pay salvage yard nearby. I got one, and swapped it out. Drove the car again, and it felt better than ever. So I figured that was the end of it.

Of course it wasn't... I just drove to the store and I got there just fine. It was when I had started to leave the parking space that it started to act up again, and the epc light came on. I hadn't even gotten out of the aisle yet that I was in, and it messed up. So now I don't know what it is. I really hope its not the ECU. I'm thinking it might be weather related, because it was raining wednesday, thursday afternoon, and earlier today before I drove the car. I looked under the hood where the ECU is, but it doesn't look like it really got wet back there. I'm gonna try sealing that area up better and see if that helps at all. Yesterday (friday) it was dry all day, and when I took it out for the test drive after the new pedal, it was still nice and dry.

If anyone has any suggestions, or has had this problem and found a fix, I'd greatly appreciate advice. I seriously just wanna burn this car down and try to collect insurance on it.. lol. Its always something with this thing...

 

Since you have a tip car you have a TCU under the carpet on the passenger side. If you sunroof drains get plugged water will drain and collect under the carpet and get into the TCU. To pull out the TCU remove the 2 screws to the kick plate near the carpet by where your feet sit and sharply pull up on the trim that runs along the side between the seat and door. Then lift up the carpet and its is best if you have a piece of 2x4 to hold the carpet up. Take a light and look in there and see and try to feel if anything is wet. You can slid the black box that holds the TCU forward and then pull the box out and you can open the box and see if water got inside. If it is wet hopefully you can dry it out and be good and try and clean the sunroof drains so it don't happen again. I hope this helps out and that is what I would check first. Good luck and come back and met us know what you find.

 

I got to the TCU. No water or wetness under there whatsoever. I looked the ECU today in the sunlight, looked completely dry in the safety box in there too. I noticed the drain holes were a little clogged up though, in the firewall. I cleaned those out just to be safe. But I tried driving it again since the weather is nice today, and the problem still bit me in the ***... I got another code that came up though. P1639 (wiki rosstech definition). Both of my codes that have come up mentioned something about the pedal, or ECU. But the new one mentioned checking the O2 sensors. Since the rear one's are deleted out and have been removed from the car, I'm gonna check on the front ones in a little bit after I eat. If anyone has any other thoughts, lemme know. Thanks guys

 

You might want to ask on Audizine or on the S4 forums. That all I could think of since your problem seem to come on after all the rain. Hopefully you figure it out and if you do please post back anderson us know the fix. GL

 

I figured it out. I messed up one of the camshaft position sensors a few weeks back. I patched it up pretty good, or so I thought. I got a couple different codes today that were for a CPS fault, so I got a new one and swapped em. Drove home with no problems at all. I'll come back in a week and let ya know if its still doin good, unless somethin comes up before then