my car is a 86 560SEL with 190K miles on the clicker.


I am still trying to get to the bottom of a hard start/rough idle condition that has persisted thru all of my other troubleshooting efforts. I have checked all of the basic stuff per the archives and good maintenance -- new injectors and seals (tested with carb cleaner for leaks and found none) , ignition wires, plugs, rotor ,cap, OVP relay, fuel pump relay , bench tested and cleaned the idle air valve .

I am starting to conclude that the defect can only now be in the idle control unit. However, i dont have a spare and dont really want to buy one unless I am more certain the fault is there.

I have tested the wiring to the icu and it appears to be good. However, I can remove the ICU from the car and the engine still starts and idles as normal (rough) indicating to me that the icu isnt doing anything. Also, when i unplug the connector to the idle air valve there is no change to the idle. The voltage at the idle air valve when connected to the icu is only 1.25 volts. The engine is under lambda control based on the duty cycle at the diag connector.

Can someone give me an informed opionion if my thinking is rational here and some ideas on how to test the icu???

Thanks.