As a new member of BMWCCA, I only wish I had heard about you five years ago when I bought my first BMW 2002. Better late than never!
My 1976 BMW 2002 chokes up periodically, refusing to idle but bucking, surging and so forth unless I keep the RPM at about 1500 to 2000. Foreign matter becomes lodged in the idle jet.
To solve it, I remove the air cleaner and the solenoid switch/valve at the jet, insert a basketball inflating needle on the end of a bicycle pump and blow out the orifice. My first precautionary attempt was to install an in-line fuel filter between the firewall and the fuel pump and this proved successful for nearly 6000 miles. The problem has returned in spite of replacing the filter every 3000 miles or so.
Author: Stephen H. Busch
The problem is the dirt. Does it come from the tank? Does it come in through the carb? Make sure that the top half of the carb is screwed down securely. Even a slight leak can pull in air (and dirt! You may have to remove your fuel tank and clean it out if the problem persists (or keep your bicycle pump handy! Tech Ed.