88 BII 2.9 A4LD:
Used engine put in a while ago. Now when I'm driving it acts as is the choke is sticking but it is fuel injected so that is impossible. It doesn't do it all the time just when it feels like it and then it goes away in a few miles. When it does it there is no power...black smoke...and no check engine light. If I put the petal to the floor it will go like hell until it shifts up a gear then drop off again. THe Wham...it goes away and everything is ok. It has bad exhaust leak from the engine swap. I'm working on that problem.
Any ideas?? Oh yeah....no codes show up.

 

If the leak is near the O2 senser I wouldn't do anything untill you get that fxed. The fresh air can make the O2 think the engine is running lean so it adds to much fuel.

 

That's what I figured. Need to get it taken care of soon. Drove 27 miles home last night at midnight and it ran great. go figure!