'92 400E irratic idle
Sometimes my 400E idles at less than 500 RPM at a stop light. Most noticable with A/C running (warm weather).
Finally noticed this problem accompanies the cruise control not working! Shut off ignition and re-start, no problem!
This morning I stomped on the gas to enter traffic and, no cruise and rough <500 RPM idle!
Now I think the belt tension is too loose and the A/C pump is slipping under hard acceleration and shutting off one of the computers.