Arthur, thanks for the reply. Search on OVP turned up some interesting possiblilties - including distributor cap/rotor.

Do try all of the electrical basics, like plugs wires cap,and rotor.be for you throw a bunch of parts at it.It is one of the first things people say to replace, the OVP.Now it dose run or supply a good number of Items so if it is bad you would have a host of symptoms.If you have the skill to use a volt meter you need to check several items, The on off ratio,The Eha, the pot, and the position sensor. Quite a few post on all those items. Good research, and good luck.JNT

There's no distributor cap or rotor on the car - so don't try to replace those.

No EHA, no rotor ..none of that stuff.
Your car is HFM/SFI , meaning full electronic with distributorless ignition.
All is controlled by an engine management ECU and that is powered by an OVP relay, which , in your case was a troublesome , faulty original part. Get the new part # and plug it in.
As I said , do a search to see if yours is original..if it is , replace
it first.

Thanks everyone - I realized soon enough that the '96 C280 doesn't have a dist cap/rotor.

I did examine the spark plug wiring and indiv coils - all of which it turns out are only about 1 year old.

The symptoms have changed a bit - or may be temp dependent. Once started, the engine RPM fluctuates from the real low 100's to slightly over 1000.

I'll also check the OVP part #.

-Forrest