I bought an 87 740 Sedan a while back for 350 bucks. It had a rough idle, but ran, sometimes emitting black smoke from the exhaust. There's oil in the intake sometimes. About a month ago, it started sporadically refusing to start, sometimes when hot, sometimes when cold. I removed a spark plug wire, put a screwdriver in the boot and had a good arc to the exhaust header, so i figured it must be something with the fuel system. I replaced the fuel pump relay, still no change. Sometimes the car would run perfectly, other times it would turn and turn and not fire up. I don't hear a fuel pump going when the key is turned, so I think it might be one of the pumps, or possibly an injector solenoid.
I replaced the entire engine wiring harness, as my old one was completely decayed. I was hoping I was dealing with some shorts somewhere, but even after the replacement, it will only start, sputter, then die. If it does decide to idle (abnormally hight at about 2000-2500 rpm?), it will only do so if I don't push on the gas, as soon as I do, it bogs and quite on me. Here's my questions and thoughts.
-Is it possible that the Idle Valve Control (under intake manifold, has hoses from case to Control to flame trap) is turned around? The Bosch lettering is on top)Is it broken?
-Is my Throttle Positioning Sensor bad?
-Is my AMM bad? (Air mass sensor thing in the intake? Has the platinum wire configuration in it. Both are intact.)
-If it is a bad fuel pump(s), why does it start, and sometimes idle?

This is my first time one here. I have always worked on my own 245 back home, and love these cars, but my friends, this 740 is stumping me. Any help would be much appreciated.
Thanks everyone, John