No idle trim knob in a W140.

There's a connector to a round device on the back side of the IP. Pull the connector with the engine running. If rpm doesn't drop, EDS isn't communicating with the IP. If rpm drops, I'd rather have bent rods

Is the tach working? If not, check the OVP fuse and relay. I don't remember where they are in a W140 or if a W140 even has them. I hope it's not one of the modules in the breadbox by the right hood hinge because they all look expen$ive. Check also the wire to the flywheel sensor behind the oil filter (quite a chore in a W140).

My guess is the AC compressor won't engage either indicating it's probably a bad OVP relay or flywheel sensor.

Being a 93, it's subject to MB's biodegradable wiring harness.

Sixto
87 300D