I had this exact exact problem with my 1986 740 GLE a few months ago. I read somewhere (probably in the FAQ on this site) to disconnect the Air Mass Meter (also called airflow meter, mass airflow sensor), and see if it will start fine then. On my model, it's connected just after the air filter in the air-intake line. There's a cable going into it that looks something like a printer cable on your computer (well, slightly older computer... maybe 4 years ago?) Unplug that (somewhat carefully) and start the car. If it runs, you have a bad AMM. New ones cost quite a bit... I got lucky on eBay and grabbed one for $50. Note that if it runs, you won't be able to go very fast or very far... it'll die if you accelerate too hard. It's a 5-minute job to replace once you have a new one that even people who can't program their VCR can do.