I am restoring a 1971 Volvo 1800E with a B20 engine fitted with the Bosch D-Jetronic FI that had been in long-term storage. It does run, so I believe that the engine mechanicals as well as the electrical system are both in good order. When I first got it going, it seemed to run fine, but now the engine does not idle properly (it pulses or cycles constantly from about 1000 rpm to 2000 rpm) when on level ground in the garage. And, when I attempt to drive it, it has very little power under load and will quickly falter and stall. It will easily restart, but runs for 10-15 seconds before it again dies. If it sits for a few minutes (~15), it will restart and run for a bit longer before it again stalls. When driving it, the longer it sits, the longer it will run before stalling, but never longer than about 30 seconds before it again stalls.

My thought on the stalling was that it was being starved for fuel, but I didn't think that would explain the cycling rpm at idle...perhaps I have multiple problems? I did replace the fuel pump and fuel filter, but it made no difference. I'm out of my league when it comes to FI. Could it be a rusty gas tank? A blocked fuel line? A bad sensor? A bad computer? I'm baffled, so I would really appreciate your thoughts?

Thanks and hope you can help.