M20B27 Possible sources of Flat Spots

[weistd]

Hi,

I just picked up an E28 525e last week. Great car, but there is a problem:

Flat spots.

When I am accelerating, it backs off at about 2300RPM, then again at about 3000 and once more just before 4000. It does this at part throttle applications.

It also used to do it at WOT, but I did a few doughnuts 3 nights ago and having it bounce off the limiter for about 15seconds or so fixed that up, so now it only does it when I have the pedal partially applied.

Any ideas what it could be?

3 possibilities that I have been told so far:
1. AFM is having problems
2. Spark plug cables
3. Injectors are dirty

Any other ideas?