Although mine is an SL, its a 1985 and the same 380 engine so I assume common parts.
I am having intemittent idle problem creeping up from 900 to 1200 in Nuetral.
I tested the warm up slide valve by applying 12V and found it was operating so I went on to Idle control module.
I took off the cover and flexed the board which made the idle settle right down. Since I have no soldering skills I replaced the unit with a rebuilt Programa. Worked great for about a week then problem came back so I had Programa swap it for another unit. Same result, good for a few days then problem returned.
Next in line is the OVP, checked and the fuse was ok. I figured its not a fotune for the part and my ABS light was on (I'll go into that later) so maybe the OVP would fix both issues. Replaced OVP, problem still there.

I now strongly suspect the problem is the wiring/connectors to the ICM. Car is bundled up for the winter so I'll have to wait till end March to confirm. I've had problems with those type of connectors elsewhere in the car where you get problem symptoms and its all because of that connector. Jiggle it and they go away. Then the fun part is trying to locate exact point that is loose/faulty.

Regarding ABS light, I didn't suspect OVP because the ABS module was doing its job - at engine start up light would not be on. Once I hit 8-11 MPH the light would go on. I cleaned the 2 front wheel magnetic sensor tips which didn't fix it. Also raised the back wheels and got them up to 20MPH - did not trigger the ABS light. So it must be one of the front sensors. Tested resistance of those sensors and just can't get a consistent reading on those guys. I think the proper test involves giving the front wheels a spin and then testing the resistance, it should fluctuate with wheel speed.