[NathanK24]

Engine is an M110.990. Finally, the car runs. The fuel pump, accumulator, filter, lines are new and tank restored. Spark plugs and air filter also new. Made sure the new spark plugs did not have an integrated resistor, since the wires already do. Once clean fuel was flushed through lines up to distributor, the car started after sitting 10-15 years. Distributor and injectors have not been replaced.

If I start the car cold, it will idle nicely. Once taking it for a drive and it warms up, when coming to a stop or very low speeds, the engine stalls. For context I did some testing while stationary. I started the car from cold and it idled fine (about 800 rpm) until it warmed up, then the idle dropped to about 550 rpm once warm and in park. When putting the car in drive and not applying throttle, the idle drops momentarily to around 300 rpm, recovers slightly, then stalls. I shut off the car and adjusted the mixture screw (3mm allen) 2 times, each in increments of 90 degrees clockwise to go richer. This did not solve the problem, and may have made it worse. Any thoughts on where to go from here are appreciated.

This plastic piece connected to the throttle actuators is also starting to deteriorate and chip away slightly. Does anyone have an explanation of this component and its replacement part number?

 

[NathanK24]

Addition: When turning on the AC, the idle speed shifts higher and it will bog a bit but not cut out when putting the car in drive. My guesses for troubleshooting at the moment are fuel distributor, fuel pressure regulator, AAV, and EGR valve.

 

[MSchnide]

Recent similar problem on my 380sl. Replacing the ICU ignition control unit (on inside fender behind driver side headlight) did resolve the problem. I replaced it based on internet advice and had no form of technical diagnosis on this issue.
In that advice, the fuel pump relay (behind glove compartment liner) was also noted as a possible cause.
With the car inactive as long as you say, you may have multiple issues contributing to the problem. Hope this may help.

 

[NathanK24]

The issue seems to have resolved itself, sort of. I replaced that bushing that is in the photo of the first post. Also, I increased the idle speed using the screw on the throttle body. Before replacing the bushing, the idle speed alone did not fix the issue, but helped slightly. Guessing it was a mix of the new bushing not allowing throttle to go below the original "zero" position at idle (0% throttle) before the bushing fell apart, as well as the fuel system cleaner doing work on any organic deposits in the distributor and injectors, which I have not touched. Car is running very well relative to before.