Another high idle thread - after cluster swap
 

Just replaced my old and faded cluster with a used one.

When I started the car idle was about 1,500 rpm.

I pulled the economy gauge vacuum line and ut it back on, no change.

Sometimes turning the car off and on again would bring the idle to normal, but it often goes back up again after a while.

Anything in the cluster that affects idling? That is the only thing I did before this problem started.

The cluster I got off ebay has the exact same part number as the cluster in my car btw.

Car is a 1989 260e.

Is the idle actually high, or is the tach just off? What I mean is - does the engine actually sound like it's running fast when the RPM is elevated?

On some of the later cars there is a circuit built into the speedometer that can potentially cause problems with properly returning to idle. Member "Stretch" has quite a posting somewhere on this forum chasing that issue down in his W201. I don't remember where I read his saga or I'd post the link. It may be in his epic saga in the Long-Term Build forum (worth reading just because!)

One thing to try is,, remove the conector for the rev counter and see if that changes anything ...The rev counter can stop the engine starting if it fails inside.Only other thing i can think of right now is the vacuum pipe is doing nothing on there .What do you see on the economy guage ? is it pegged to the left on start up ?

Diseasel, yes it really is idling higher, around 1,200-1,300rpm, not 1,500rpm like I posted originally.

Optimus, the vacuum line was vacuming when I pulled it. I dont recall if it was pegged, but it was moving around while I was driving.

Interesting about the tach affecting running, will check it out.

Apparently solved for now!

I brought it in to an indy, who unplugged the ECU while it was running, then plugged it back in. Problem hasnt shown up since.

I talked to him about the rationale behind it and he said he just does it to a lot of M103's with weird running issues and it solves some of them.