All this started with with a hard to start car with ABS light on. I had a blown OVP fuse in my 1990 300SEL, I replaced the fuse and the car idles 1600 rpm and is easy to start, when i remove the good fuse, it idles normal but is hard to start. I Know the OPV will have a lot to do with hard starting, here's my question. What i have found is that when i disconnect the idle control valve, the car idles at 600 rpm and runs normal, with it connected it idles high. Is there a problem with driving with the ICV unplugged or will it affect the cold start value? I drove 10 miles today with it unplugged and all seems fine. Another questions is how many volts should be at the ICV, i am showing 2.16 volts. I have also cleaned the ICV and when i put power to it i can hear it operating, 12 volts only, with it connected i cant hear it operating with 2.16 volts. Not sure if all has to do with the OVP relay or not, I tried to find one at a salvage yard today but no luck.

Most likely you have a sensor input issue with the fuel system, causing the high idle.

Leaving it disconnected won't cause many problems.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Update, I replaced the OVP relay new from Mercedes, no change. I have also noticed the last few days in the mornings that the car doesn't want to change gears when cold and i can hear a loud sucking noise, almost sure it's the air intake. I plug the ICV back up and it shifts fine and noise goes away. After it warms up i just unplug ICV and all seems fine. Like you said, there shouldn't be an issue but i would like to pinpoint the issue. Thanks

Up-shift delay is normal in cool/cold weather & has nothing to do with how the car idles.

Testing the air-flow position sensor is a starting point, hope you good with volt/ohm meter.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Ended up being throttle micro switch, but ever once in a while right after starting up i will still hear that loud sucking noise and car doesn't want to change gears. i have also noticed sometimes after i let off the gas coming to a stop the sucking noise comes back and will go away after i accelerate again. After starting sometimes it will go away when i put it in a different gear of i might have restart the car.