My '89 300E will go thru cycle of not idling when I decelerate at stop, so I use left foot on brake and right foot to keep slight pressure on gas pedal so RPMs are 600-700. Engine often idles rough at this time also. Goes thru cycles of doing this several time then will run well -holding idle above 500 without problem. Had MB mechanic drive it for week. Eventually happened 3-4 times and always restarts easily, but by the time he got back to shop it was OK. Could not find problem. MB dealer put it on scope, and gave estimate of $2,500 to tune-up, replace parts such as lamda tower, injectors,etc. but would not guarantee that it would be fix. Said it could be many components including climate controls, fuel pump, etc. Earlier problem w/engine dying at road speeds fixed w/fuel pump relay switch. This problem when engine should idle. Cleaned trottle linkage, added cleaners & gas-line antifreeze to tank.

Notice that dash lights dim when RPMs decline. Alternator rebuilt 1 yr ago. It would appear to be related to some electrical switch since it dies fast and one has to be quick to catch it or it dies. Big problem in traffic.

Any recommendations? before I have to take it out and shoot it.
Thanks.