My 89 190E 2.6 has a rough idle that almost chokes out, including a slow fluttering sort of rpm increase when depressing the gas pedal .
There are 180K miles on this engine and I have just replaced all 6 injectors, rotor, cap, plugs, CPS, and electric coil .
I can run the engine at normal speeds without feeling any rough running, including testing passing acceleration on the open road with the tach sometimes going to 7K before changing back, all with no apparent engine stutter, missing , or other issues.
I have read a lot of information here about causes but I don't have any dash sensors lighting up saying I have a problem, like the engine light that might come on when an O2 sensor is going bad.
For my first problem analysis, I have checked all the vacuum connections and no noticable issues. I have cleaned all the acclerator linkage and checked all electric connections.
At this point, I removed the Idle Control Valve to watch if that worked when just turning the ignition key to the on position. I saw the ICV click to a wide open position and in a couple of seconds, click back to mostly shut . I don't know if that's proper or not.
Next I just sealed a piece of copper tubing where the ICV was to see what happens and the car started, ran at 1,500 on the tach , but started oscillating every second between 1,500 and 2,000 like someone was stepping on the gas and letting off at a consistent rate . I don't know if that is supposed to happen when there is no ICV or not ?
I replaced the ICV and tried to just electrically disconnect it. The car started and it idled the same at about 950 on the tach. Nothing seemed to change in idle speeds between the ICV being connected and not connected, but I didn't do any additional testing.
There was one real odd issue that I don't know if it is supposed to happen or not and that is, while I was watching / listening to the engine idle, I once noticed the Mass Air Flow unit plunger open ever so slightly for a milisecond, so I tried to see what would happen if I pressed down on the plunger while idling. Each time I so much as touched the plunger, the engine would choke out and shut off ? I don't know if this is supposed to happen.
At this point, is there anything that sounds like it is pointing to something faulty that I can further try to debug the rough idle issue ?
Thanks in advance for any help,
Padge

 

Sorry I never followed up though noone ever answered either ! I removed the Distributor Cap cover , waited for nightfall, started the car, and noticed a small spark at one of the Distributor Cap nodes. Turns out there was some sort of misconnection between the Sparkpug wire and the terminal where the metal piece of the wire end was actually not in the slot but on the outside of the Dist. Cap node !! The electrical charge was still going from the wire into the Dist. Cap but burning a hole thru the node !!! Replaced Dist. Cap, made sure the Spark Plug wires were actually inserted in the Dist.Cap nodes correctly and it ran like a charm.