My 1993 400E is stumbling/ running rough at mid throttle. It starts up and idles fine. It seems to run well when the engine is cold, but problems show up when it is warmed up.

I checked for DTC's with my Trisco/ Palm scanner, and found no engine codes set. (I did discover an ABS code, but I haven't tracked it down yet. My wife isn't currently driving the thing until I get the running rough part fixed. She's taken over my Tundra Double Cab until I sort this out... One of the sensors for the front wheels is dead, apparently... As soon as I fix the engine, I will track the ABS problem down.)

It seemed to be a lean miss, so I immediately suspected the EGR valve opening too far or too soon. The problem only occurs at mid throttle, and the EGR is out of the loop at idle and full throttle... Replacing the EGR didn't cure it, though.

The fuel pumps, spark plugs, caps and rotors, oxygen sensor and EGR valve are all new, or new in the last three months. All were replaced with Bosch parts (except the EGR, it was a Pierburg egr valve) most from the dealer. The car runs great except for this mid-throttle miss... I did clean the MAF hot wire with some MAF cleaner... No change... I looked for any kind of vacuum leak, but can't find a thing.

I am at a loss as to what else may be wrong. Maybe one of the coils? I don't know... When the car is climbing a steep hill you can really feel it, on level ground it seems to run pretty well to where it is not really noticeable unless you are looking for it.

What else should I be looking at? The car should be running great like it always has for the last 160,000 miles, but it just doesn't...

sigh...

Somebody please point me in the right direction, I am out of ideas as to what might be wrong with it...

Thanks,

Kelly

1993 Arctic White 400E