Just posting for general information since mechanics could not find the problem and may be of help to someone else. Had intermittent starting problem with 1991 190 turbo. Once started would continue to run, with occasional galloping idle and stall if you did not kick the gas immediately. Usually started in morning and then not start after being driven. Would start after cooled down for an hour or so with the worst case being overnight. Left with one mechanic for a week and he said would always run when he tried to diagnose the problem. Was at another auto repair shop when it would not start for me, so left it there for two days, and they at least isolated it to no injector pulses, but then it would always start so they could not continue to diagnose. Prior to that, I replaced rpm sensor, F1 fuel relay and checked a host of other items such as the injector power stage unit and appropriate connectors for broken wires or corrosion.

A couple of days after having car back from last mechanic, idle went irractic and stalled and no start. I let the car set overnight and still no start. Decided to remove the cover from the radio suppression relay on the drive side strut tower and cleaned the contacts. It started immediated after plugging in the relay. So I order a relay from Swedish Engineering in Ann Arbor, Mich., which they had in stock and arrived the next day. Have not had a problem with starting or idle for weeks now.

Hope this helps someone in their frustration.