When I made this post over three months ago, I thought the problem was solved. However, not the case--yet.

I've now replaced everything from the fuel pump/filter/accumulator forward--except for the warm-up regulator (WUR) to try and cure the stumbling problem. This includes injectors/holder/o-rings and fuel distributor. The car is running rich, as well as continuing to stumble. Start it and, after a couple minutes, the plugs are fouled horribly. The richness and fouled plugs are probably the cause of the stumbling.

Interestingly, I bought a rebuilt fuel distributor from John at SpecialT Auto. When it was installed, the fuel mixture got even richer than with the old FD. So, the mechanic is considering removing the rebuilt FD and reinstalling the old one. Don't know if John will let me return the FD for refund. So, I might be out $449.00 as a result. John says the problem is most likely in the WUR.

The car hasn't been started for about three weeks now, but has just been sitting in the mechanic's garage. Since the last start a new fuel pump (which I had on hand) has been installed. I picked up a new O2 sensor from Phil (Fastlane) and that, too, will be installed.

Went down and talked to my old Mercedes mechanic at Quality Imports in Fort Walton Beach. He, too, seems to think the problem is the WUR. He also said the car probably needs an O2 sensor, but a bad one would not cause the car to run as rich as it is. However, my current mechanic is balking at installing a rebuilt WUR. Says he doesn't want to throw parts at the problem. That's almost funny at this juncture, since just about everything in the fuel system is new at this point.

In retrospect the best approach would have been to take it to the Mercedes dealership and paid for a diagnosis with a CIS tester. This would have been $99.69 for an hour labor. However, the dealership tried to screw me royally for front-end repairs the last time it was there for an alignment. The front-end man listed $4,300 in repairs that needed done before he could align the car. My current mechanic did the needed repairs for $700.00. Since the front-end guy wasn't going to diagnose the current problem, I should have gone that route.

This has been an expensive lesson and it's not over yet.

__________________
Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000