'93 E320 coupe idle problems

OVP relay check .. 000 540 52 45 changed to 000 540 67 45 See if this part has been upgraded. Your car has access to codes under the hood Check the codes if you want specific possible fault conditions of the engine ECU management system.

Yep... OVP is my first check too.

Yep... OVP is my first check too.

Nobody can be absolutely certain without having there hands/ears on the car...

Did you flush out all of the old gasoline? This could be your whole problem.

Make sure there are no leaks in either the air intake or vacuum systems.

Put a bunch of the highest octane fuel you can find in there and run it till it's empty...\

They refuel and retest.

Marty

The car has biodegradable engine wiring harness - it may cause very strange and hard-to-diagnose symptoms. Now that the car is over ten years old, the wiring insulation begins to crack and cause shorting. The mechanics who know this issue won't even start diagnosing the car unless the original harness has been replaced. Check the wires going to the idle control valve (throttle actuator). It's also possible that there's another (than wiring) problem with this part, a stuck sensor etc.

flwgrsp

This also seems like a good theory for a car which sat for couple of years.

Basically the battery could be marginal, and since at an idle the alternator isn't putting out that much juice, the battery could be driving the system into a low voltage state which causes all of the electronic whoohaws (technical term) to get edgy.

You could measure the idle voltage with a voltmeter, or just try swapping in a new battery.

Marty

mentioned and will report to this group.