OM601 idle shake - PeachParts Mercedes-Benz Forum

JHZR2 · #1 02-17-2023, 02:48 PM

I just bought a like new w201 1985 190D, CA model, AT. I’ve never had a w201 before, though I know there are similarities with my other cars.

One thing that I noticed immediately was that the idle is too low. It idled a bit over 500rpm on the tach, and when I pulled the EDS electric connector, it drops a bit below 500rpm. The sticker says 720rpm IIRC.

So I need to increase the base idle. I’ve done this on 602/603 engines with great success, and even on other vehicles. I did this, got the idle up to about 550, and with the idle electric connector connected, it was idling hot around 720. But after some driving, it seems to be back to idling around 550 with the connector attached.

Additionally, even with the idle still too low, now the idle seems half time nice and smooth (with or without AC on) and half vibrating too much. In other words, say I’m driving on the highway for a long distance. Say I stop every 100 miles. Some times when I stop and it idles, it is smooth as can be, still a bit slow, but it’s ok. Other times when I stop and it idles, it vibrates a lot so the hood is shaking a bit. AC is not the cause, nor is being in drive or not. I have no evidence that the EDS system is sporadic. I also have no evidence of any issues with the fuel system.

The car runs great, and cruises at speed all day long. I drove it part way back home, around 1600 miles, it climbed mountains across CA/AZ/NM with another person and a trunk full of spare parts, and it ran perfectly and gladly did 70+ mph. It’s super clean and in great shape. So I’m hoping I can fix this in a straightforward way. I haven’t checked engine mounts yet.

Any thoughts on why despite raising base idle, which worked fine on 602/603 engines, why I can’t quite get the idle high enough to stop cold vibration.