Hey everyone, so I had my (a4) transmission rebuilt back in September, it was fine for a couple months then i ended up burning up 3rd gear and took it back, they rebuilt it again, this time they put heavier duty parts in as well as a shift kit and it ran perfectly, however I remember one night the car was acting as if 3rd gear had gone out again, I took it back home and let it sit over night. When I got back in it the next morning it was shifting flawlessly again, and have been every since. This morning the problem occurred again, it'll shift fine one minute, the next minute, I'll have to drop it to 2, pick up a little speed and up shift to 3 to get a proper shift.
I can only think of a few reasons for this happening (and I may be completely off but I'll throw em out there anyway) 1. I have longtube headers w/cats and no tune, (and yes the CEL came on) Could not tuning your car after headers make it act up like this? 2.BCM. I know for a fact my BCM is faulty (pass. Window gets stuck sometimes, radio fades, security light etc) Could this cause such a problem? 3.Car needs tune up. I've had the car for going on 2 years now, and haven't had it tuned it up since the 1st week I got it and considering I've already put over 40k miles on it I'm pretty sure it could do with one lol, but could that cause a transmission to slip? 4.MAF needs cleaning. Just throwing this one out there. The car is a 99. Please give me some input before I drive this thing off a cliff!

 

Pull your codes. There may be a clue there.

A transmission improperly filled or low on fluid can cause some strange shifting. Check it with car raised, idling in park, transmission temp at 122 F, fluid should be at or dribbling out the fill/ level check plug. Don't remove the plug unless the engine is running, transmission in park.

 

Hey guys thanks for the input. So I checked the fluid level, it's good and there's no leaks.
I checked the DIC and got 2 codes for the PCM
1. 10-pcm p0420 HC
​​​2. 10-pcm p0430 HC

Can you guys tell me what those mean?

 

Those are codes for right and left catalytic converters not operating efficiently for some reason.

Check this link, two videos.

 

As of right now it's running fine but I'll definitely check for codes if it does it again, I feel it may be because I haven't tuned it yet, There's a well known tuner in Vancouver WA. (about 20 mins away) that I plan on taking it to for tuning so I'm pretty sure he'll know if it's pcm related. Thanks for the help guys it was much appreciated.

 

Hey guys. Turns out it was the torque converter that was giving me problems, car is currently in the shop getting a higher stall converter (3000) as well as 3.73 gears installed. Thanks again