1987 560 SEL WON'T START

[Land O'Lakes Fr]

I've searched the forum every which way first, but:

Car is pristine with 87K miles, zero rust, acquired last month. Ran flawlessly, about 24 MPG.

Driving around 60 MPH, slowed down to turn right onto another road. Engine stalled. Would not start. 15 minutes later, it started but ran rough, but was able to get back on the highway and drive 60 MPH, but could feel intermittent miss/jerk. Slowed down for a red light, stalled again, would not start, had it carhauled 75 miles home.

Next day would not start. Replaced fuel pump relay with a new MB part 3 days later. No start. Bought 2 fuel pump relays so tried the other new one. No start. Both fuel pumps energize with key in ON position. Loosened fuel intake at fuel distributor, fuel gushed out with key in ON position. Loosened connection at cold start injector (if that's what it's called, has what looks like a solenoid actuated valve), fuel gushed out with key in ON position. No start.

Replaced distributor cap and rotor with new Bosch parts. No start. Overvoltage Protection Relay examined, fuse OK, jumped female terminals 6 and 2, could hear idle control valve doing something. Put the OVPR back in, turned key to ON, again could hear idle control valve doing something. Concluded OVPR OK.

Removed a spart plug, dry. Connected a snowmobile plug to plug wire, placed plug body on a new ground, cranked engine, spark looked fine.

There has to be a hierarchy of likely solutions, and I would be glad to pay a member of this forum for techinical assistance and troubleshooting procedure layout. Time is money.

Thanks in advance.

Land O'Lakes Fred