Need help troubleshooting my 300E which won't idle please.

[Gebhard]

Hello All,

I have a 1988 300E that idles rough, and dies intermittently. Some days it won't die at all, other days it won't stay running at a stop sign unless my foot is on the gas.

I read a lot of the posts here and have started troubleshooting, but could use a little help.

I checked the OVP relay (Pin 3 on the round test socket, supposed to be 2.5 to 5 volts I read) Mine measures 1.8 volts. Do I need to replace the OVP relay?

I also checked what I believe to be the lambda adjustment (Pin 3 on the round test socket supposed to be 55% duty cycle I think) Mine gives no reading (00.0%). Is this an error code? I disconnected the battery ground with the ignition on as I was told this would clear error codes. No change to the 00.0% reading. Any ideas?

I see three relays near each other behind the battery.

1) Silver with a 10A fuse on top. Part# 201 540 32 45. Appears to be Mercedes genuine part. This is the OVP relay, right?

2) Black relay marked "KVS Kickdown" Part# 002 545 52 05. This one also appears to be a Mercedes genuine part, but appears to be used as it has "300E 124/86' written on it in with a paint pen. Which relay is this?

3) A black relay marked "KAE Relay" 3.701.130 12*99 PA6 GF-30. This appears to be a non-Mercedes part. Is this the fuel pump relay or a different one?

Also, where is the decel micro-switch located. Apparently this could be the culprit also.

Anything I'm overlooking? What should be my next step?

Any assistance greatly appreciated.

Thanks,
Gebhard