Idle speeds up by its self. 1984 190d (W201) 133.233

[hsmith]

I've had some idle problems lately. Several times I have turned the adjustment nob on the throttle cable to increase/ decrease the idle. When I adjust it up to a good idle it is as if I was in the car pressing down on the acclertor. It just starts to speed up by it's self and then I have to turn it off. I look at it happening and just can't figure out what coiuld cause this.

Hugh Sr.

1984 190d (W201) 133.233

[Stretch]

Your OM601 engine is similar to the older type Mercedes engines but it has more fancy stuff on it to help it perform a bit better (and probably reduce emissions). It is essentially a mechanical system with extra (modern!) complications...

...the FSM makes mention to a vacuum induced high idle based on coolant temperature. There's a difference between manual and automatic transmissions.

(Direct link to the free and legal FSM chapter here =>)

http://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/60006.pdf

Happy reading

[Petar617]

You are not supposed to adjust the idle by shortening the throttle cable. Loosen the nut locking the vacuum diaphragm assembly at the top rear of the pump and turn the vacuum unit CCW to increase the idle or CW to decrease.
Page 25 on that document.

[hsmith]

Thank you. Hopefully I can follow the diagrams. The diagrams remind me of a test I took when I joined the Air Force.

Hugh Sr.

[Stretch]

I know exactly what you mean I took similar tests