Another 560SEC question
 

Thank you all for all the answers to my question about shocks. My 560 idles at over 1000 rpm all the time. Probably IAC or warm up valve. More worrisome than that is its stalling problem. At times at a stop or even while at speed it just shuts down and rolls to a stop. It then restarts and is fine for a few days. Any suggestions appreciated.
I also have an 85 300CD turbo that a previous owner converted to a four speed stick. Has anyone heard of that being done to a 560SEC. Would parts be available in Europe? Would the car's computer understand or rebel? The 300CD was done using all Mercedes parts.
Tom

MB never installed a manual trans on any V8 since 1980...AMG did that though $$$

The idle valve is the most likely problem.
BUT testing the circuit would be my starting point.
Making sure that the idle contact switch was closing &
that the accelerator linkage was "free" and allowing the idle contact to close.

Shortly after getting my '87 SEL (160K mi.) I had a similar problem with the car dying - fortunately not at-speed, mostly at stops. New fuel pump relay solved problem.

Is there any type of hierarchy of possible causes for problems like this? What's the most common problem, second most common, etc?

I know a friend has stalling problems with her 1990 420SEL and there were a number of possible causes. We still have not covered them all, and it's still stalling on acceleration unless the car is fully up to temp.

Check the throttle linkage to determine that it permits everything to return to full idle (all stops are contacted). Frequently, the linkages are bent/misaligned such that the idle stop is not contacted. I would remove all of the throttle linkage balls from their sockets to determine if the engine idles at the proper speed. If it does, then one or more of the throttle linkages are bent/misaligned. Don't condemn the idle computer/idle vale until you have performed and passed this test. Mark

I say Idle Control Unit, Fuel Pump Relay or EZl is suspect. I had the same problems and on one car the ICU was bad and on another it was the EZL. The linkages can be a problem, but more often it's electrical. and the shut off and rolling to a stop is what my SEC did when the EZL went south. left to get cold it would start and run fine for an unknown amount of time and just die. A good used FPR fixed the other car.
Sounds like you may have two problems, one ICU(idle) and the EZL (dying).

try cleaning the idle control valve with brake cleaner,check the current of valve should be around 700ma to 1000ma also the voltage is around 4 to 5 volts. check for vacuum leaks especially around the fuel injectors seals get hard and leak use wd40 squirt around each injector if the idle drops you found vacuum leak.. stalling! fuel pump relay common problem.. EZL cutting out possiblity but if you replace this part make sure you install new ignition coil they cause the ezl to fail...this is just a few things to check
Bob