I've noticed that at speed when I'm running at full throttle (3 to 5k rpm) sometimes the power seems to dip briefly then come back again, it sometimes happens several times as the revs slowly rise to create a pulse type effect. The power dips are very smooth, but there's definitely something wrong. It may happen at lower speeds under full throttle, but when the engine is accellerating quickly (in lower gears) i haven't noticed it. Anyone got any ideas what may be wrong?

Could be the tranny chip in your '91 - there was a service bulletin issued to fix an issue that sounds a lot like yours.
I had a weird surging like similar to yours and found that my chip had not been changed out - $15 later and voila-all was right with the world

Thanks Rocky, where is the transmission ECU located? It's not with the DMEs/EML and i've no idea where it is? How do you know if your chip has been updated? Sorry for the barrage of questions but you've got me all excited!!!!

Same compartment as DME's.

right side trunk compartment=EGS for transmission.

Ooops! always forget about that Bosch box?

Elektronisches Getreibesteuerung = Electronic Transmission Control

Thanks chaps, i wondered what that was in the trunk.... So i'm guessing that i need to take it to pieces and get the serial number (or similar) from the chip? How will I know if it's the "good" one or not? Should I contact BMW?

These units are year specific. a 1991, 1992 unit will NOT work in a 1993 and vice versa. If it is indeed the EGS, it can be reporgrammed (been there, done that) -I paid about $150 for this service locally. After it was reprogrammed back to specs, car ran like a champ.

I have had corrupted EGS reprogrammed also for my '92. Apx $250. for me, works like a champ. You can send yours to goecm dot com for checkout/reprogram. No alliliation ,they just did a good job for me.

Are there any more symptoms of a corrupted EGS? It's a fair bit of cash to drop when I'm not sure it's the problem? I've just bought a OBD-I diagnostic cable and when i manage to get a second serial port on my laptop (via a USB converter) I should have it working. Will this shed any light on my problem?

Rockytt, what exactly did you buy for $15? I like the sound of whatever that was!