400E looses power when accelerating
 

This is a '93 400e with some 128K. Originally started having intermittent power loss while accelerating, which later escalated to very rough idling. No check light, no problems starting.

Replaced ignition cables, plugs, rotors and distributor caps. No effect.

Replaced upper wiring harness. Idling is OK now. Acceleration OK for a few miles then starts acting up but not as bad as before. Feels like half of the cylinders are off.

Any suggestions would be appreciated. I'd like to avoid replacing the large wiring harness if at all possible.

Alex

'93 400E
'95 SL500
'90 RR County (yes, i am a masochist)
'99 RR 4.6 HSE

Engine Wiring Harness
 

It could be the engine wiring harness. If it is, you will want to replace it ASAP or it could fry the ECU. That's what happened to my 93 300E (M104 2.8L engine) a few weeks ago.

Well, these cars are known to have that problem (biodegradable wiring harness).
You can do a search in the forum, and read many postings, see pictures and learn the instructions on what problems to look for on the harnesses.
Then you can determine with a relative degree of certainty if the harness is the problem or not.
Another thing that comes to mind is the ignition coil.
IF you are unwilling to take the risk, my suggestion is to bring the car to a good MB technician and have him determine the cause of the problem.
IMHO.