those rough idle blues...
 

In pursuit of the hunting idle/stumbling/stalling problem on my 87 300e, I have come to the conclusion that it's highly likely bad electrical connections are the cause of this intermittent nightmare. So far I've identified bad cracking cables and connections on my Idle Control Valve and, today, the EHA valve. I've replaced the connectors and am now considering replacing the entire engine wiring harness if I can find one cheap.

Obviously this isn't the whole cause, I've also had to replace cracked vacuum hoses and a stuck ICV, corroded relays, injectors and fuel accumulator in the course of the battle but its something to watch out for, particularly if the problem comes and goes without apparent reason.

I know the early 90s cars have that degrading harness issue, but this seems to be simply down to old age in a hot, harsh environment on a 16 year old car.

Hope this will be of help to all you 300e owners out there with idle problems.

I just fixed my rough idle last week. In my case it was a vaccum.

I know most shops will automatically change the wiring harness when these cars come in with idle problems.

After changing the wiring harness yourself, I'd start with the simple stuff....fuses, vaccum hoses, connections, etc. Then do some of the inexpensive DIY stuff....change the motor mounts, clean the ICV, etc. If that doesn't clear it up you may have to take it to the mercedes dealers for a diagnostic....then decide if you want them to fix it, or take their diagnostic and fix it yourself.

Good luck.

Oh, its Ok, I've fixed it already. In fact I've been fixing it once every four to six weeks since I bought the car last year :)
Just hoping that this time I've found out why it keeps coming back.