i'll start from the beginning - 'tis a very good place to start....
My brother in law used to have a wrecker/towing business - he towed an '84 318i and an '85 318i.
the '84 had a head gasket problem, and the '85 wasn't too bad apart from the radiator being shot.
To cut a long story short, the '84 is the only one with the good title, so that's the car i have to run.
I took the head off to replace the gasket, and found out that the head was cracked. So i replaced it with the head off the '85 model. I put it all back together and it seemed to be not too bad for a basically rebuilt motor. It was a little rough, and i put this down to needing some run in time and old parts.
At this point, it had a really rough idle - if at all, and seems to misfire.
After much Tender Loving Care, and 300 miles, and new filter,oil,air filter, plugs wires it still misses. I've gotten the "best" of the 2 cars, idle control, coil, air flow sensor, barometer and none of this seemed to help.
I've checked all of the vacuum tubing and that seems fine. It's had 2 or 3 injector cleaner liquids gone thru it.
Despite that, it seems to run fine - i haven't got an accurate MPG figure yet, the speedo cog still needs replaced.
The other problem i have.. is when it gets driven at high RPM, 5k-6k range, and then the motor is stopped a few miles later, it will not restart no matter what i try... i've tried swapping ECU from the other car and nothing... and when run without it at least fires and runs for 5 seconds. Leaving it overnight seems to be the only thing to do.
SO to cut a long and many dirty hand hours short, it runs rough at idle, and why it still misses.. if anyone has any idea at all, i'd be much obliged!