Ken has a good point --- 1986 was among the years of the "biodegradable" engine harness (though I'm not sure if the 740s suffered this problem in '86 as did the 240s).

I'd examine the harness for evidence of the insulation crumbling and falling off. Follow Ken's suggestion and look for a bad ground or shorted wires (tough to do....).

If you decide to check the temp sensor, remember that your engine has two of them. The first sensor is for the gauge (single-wire device) and is located under intake header #2.

The second sensor is for the FI system (two-wire device) and is under intake header #3. It's difficult to access. A failing sensor could have a high resistance, which would fool the FI ecu into thinking the engine's colder than it really is. The ecu will send extra fuel to your "cold" engine.

If the sensor connection breaks, causing infinite resistance, the ecu will think the engine's minus a zillion degrees and POUR in the gas, flooding it, stalling it, and filling the crankcase with fuel (BTDT).

Yes, a dirty throttle body can cause crummy running, particularly at low speeds. But I don't think you'd get the type of problems you've described. Your problems sound like crossfiring in the ignition or mis-timing (cam and dist go together on your car).
--
Don Foster (near Cape Cod, MA)