Easy OVP test?
 

'86 190e 8v. Cold start and disconnect EHA. Car dies. Same if you disconnect the IAC. Is this proof the OVP is working?

I think the best way to test the OVP is to find a 10 amp fuse(s) you know to be good install on the OVP relay and see what happens on a cold start, then if the start is the same (ie poor) I reckon that proves the OVP is a goner. If the start is good then the old fuse(s) must be bad. Well that sounds logical enough to me! ;)

Mike.