low idle in D and R (300E)

[JEdwards]

First, let me say that I've done a great deal of reading already and have learned volumes about this car compared to what I knew before finding this site.

Car: 87 300E

Symptoms:

Car idles fine in P and N, constant 650+/- 50rpm per MB specifications

However, idling in D and R is a constant 500rpm now after playing w/ the mixture a bit. Previously, had touched EHA setting (per another thread advice, terrible idea). As a result, my mechanic (who is an older guy that has several of these cars) adjusted the mixture to make the car idle perfectly in P and N, but D and R were rough and stumbled on acceleration. Now, w/ the new EHA, the car idles at 500 RPM in D and R, but doesn't stumble on acceleration. The Economy gauge isn't measuring properly and the engine doesn't sound right with the low idle, like it is going to stumble.

When I asked my mechanic about it, he said the problem was linked to the transmission wanting to drive the car and the engine not being able to do so, thus a rough idle - and "these cars always have idle issues".

I don't really know what else to do, but can tell you that I know the car needs motor mounts (which may/may not affect idle, or so i've read), and can't seem to find anyone w/ the same problem as me - there is no surge to 1k rpm, its just a low idle with the economy gauge all screwy.

Should also note, the car drives fine right now, but doesn't seem to have all the power it did before i replaced the eha valve tonight.

Whats been done:

-checked for vacuum leaks at breather hoses
-replaced cps
-replaced cap/rotor/plugs
-replaced EZL module
-replaced EHA
-played w/ air/fuel mixture
-replaced OVP
-replaced FPR

Thanks for your help.

[JEdwards]

bump

(thanks to Mark's million posts about the same issue)

[slk230red]

Have you looked into your Idle Control Valve?

I'm having the same issue with my '93 109E 2.3. The cars starts and runs perfectly, except the idle drops to 500 to 550 rpms in drive with the A/C on.
This much I do know, the Idle Control Valve is not operating. When I turn the ignition on it doesn't click, when it is running and I unplug the connector, it doesn't affect the idle. If I apply voltage to the ICV, it clicks and the idle rapidly increases.
With the ignition on, I have 11.15 volts across the ICV connector. Pin number 2 (plus side) reads 11.91 volts, which according to my schematic it comes from the OVP relay. The ICV has 8.8 ohms of resistance.
I'm stumped up to this point. The ICV will operate with a 9 volt battery touching the contacts, or 12v applied from the car battery.
I have replaced all hoses going to and from the ICV and took it out and cleaned it, although it looked very clean inside.

Let me know if you find the problem with your low idle.

Thanks,

Dave