1987 BMW 635

Engine Mechanical problem
1987 BMW 635 6 cyl Automatic 199000 miles

My 635 sit undriven for about 3 weeks. When I went to start it the battery was died. I tryed to jump and it took several minutes until the battery took enough juice to start the beamer. Once I got the car started I let it run for a little while Iturned it off. When I tryed to start it again the battery was to died to restart the car, so I took a battery out of a different car and put it in the beamer. The car did start right up, but died within a few minutes, I thought it might have been low on gas and that was the cause. The next morning the car start right up, I drove to a gas station less then a mile from my house and got gas. When I was leaving the gas station the car died at the stop sign but start back up after it turnover a few times. When I got to the next stop light the car died again and would not restart, it turned over but wouldn't start. Later I came back and the car started right away but died again when I came to a stop sign, after sitting a few minutes it started when I tryed to give it more gas while I was driving it would pop and backfire but it did go faster and I drove the rest of the way home.
I have tryed and checked varies things and I think I have ruled somethings out like the fuel pumps, filter, I have checked for vac leaks or loose wiring.
The thing I don't understand is that the car ran fine before the battery went died after sitting for a short time. I am wondering if having the died battery or trying to jump the car did something.
I really can't figure this out, anybody got any ideas?
Thanks for your time
April 11, 2009.

I noticed when idleing it idled at about 800 rpm but when I put into gear the rpm went down and then would die. Sometimes it would start after and sometimes not. I know the idle is not adjustable but thinking it is all related.

Apr 11, 2009.
Sounds like it is time for an inspection II. The problem might be an idle control issue.

Dr. Hagerty
Apr 13, 2009.