Sometimes we hope that MB would design systems so that we can figure them out but not always! Since I've had to repair many of these cars with ASR & "CIS", I can tell you that a pin-by-pin test w/fault present is the only way to diagnose. Since the system only acts once in a while you probably wont find fault. Many times at dealer we would install potientiomer for test driving. And since you've done pin-by-pin testing already & haven't found fault this is the most likely failed part. Sometimes the throttle actuator causes the same problem. The actuator is simular to newer throttle actuator on the HFM & LH engines, we all know how often they fail.
MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V
[This message has been edited by M.B.DOC (edited 07-16-2000).]