BMW Repair: BMW 318i 1984 starting problem, mechanic check, bmw 318i

Question
Ok, this could be a long list of possibles but I need to start somewhere. Had car stolen so brought this car to get to new job. Had to replace radiator and I replace battery/plugs so far. Car originally used to rev/drop/rev loud and drop for 2-3minutes before idling ok. Then a week later while driving it wouldn't go over 20miles an hour. When cold it would run ok, I'd drive to border, but by the time I got through 1hour later, it again wouldn't go over 20 mph. So I was desperate and unplugged the connection at a part I believe is an oxygen mixture device. When I put it back on, it all ended up being fine. But somewhere along the way, I must have "changed" the screw setting that adjusts mixture, because the rev/drop problem disappeared. Car ran well for days, but today it stalled in the middle of the road. Under hood, looked like 3rd cable to spark plugs was off. Replaced, but now the car still wouldn't start. Battery new.
Question 1: anything I can check I'm not thinking of? It sounds like it is not getting gas or not getting a spark.
Question 2: If I need to take it in for service, what should I have the mechanic check/do to assure this car is drivable later.  Sorry for this type of description but let me know if you need more details.
thanks
duane

Answer
the idle flucuation is usually the idle valve and idle control unit need replacement or you could clean the inside of the idle valve first. the cutting out after driving could be a clogged cat converter. to check this you must remove the o2 sensor or part of the exhaust before the cat to see if power returns. this will be very loud.
                        Kimber