car is an 86 s4 when im accelerating in 1st or 2nd gear the car hesitates around 3500 rpms and the acceleration slows down a little without me ACTUALLY deccelerating. after around 4000 rpms it proceeds and accelerates smoothly. but i was wondering why does it struggle around 3500 rpms?

 

This is common on 7's. The obvious answer is to check the grounds. The secondary injectors turn around that rpm which could be causing the problem.

If you used your title in the search thread you will find lots of post on this subject + an anwer.