not sure what sort of ECU they had on 1984 318's, but are you getting a check engine light?
once again, my knowledge on the M10 motor is...not very good. but O2 sensor? Check throttle body for blockage? the car might not be getting enough air? or spark.
how old are the wires? did you check to see if you are getting a good spark to the plugs?
black smoke means you have burning oil, so check if the plugs have oil on them. if so a gasket may need to be changed.
also check vacuum lines. they might look fine, but squeeze them a little to see if they are deteriorating. this can cause bad idle/not running if the leak is bad enough.
We all get the urge...Saturday early morning...nothing to do till noon...
The aural sensations of 1st gear WOT
**CGM **(Certified Garage Mechanic)