240 mystery!

1. if you have access to a known good air mass meter, switch your out and put this one in, and reset any 'engine service' faults. if this corrects your problem, then it's time for a new air mass meter. though this part is a little expensive, it's one of the easiest to diagnose.

1. if not a problem with air mass meter, then try cleaning the throttle body and body orifices. any decent haynes manual will walk you through this.

2. last year, on my 91 240, i needed to replace some kind of idling valve. since this was past my diagnostic skills (see #1, #2) this was diagnosed and performed my dealer (ouch!).

Have you checked the ECU codes to see what errors it is giving? They may point you in the correct direction.

AJS

It sounds like a restricted (clogged) fuel filter. When you shut it off, the line pressure slowly comes back up, only to fall again as the filter isn't able to er, pass enough gas to supply the engine's needs. Just a theory.

The only component you seem to have missed is the flywheel sensor.

I purchased (for a song) an '86 Volvo 240 that had this exact problem. The previous owner had had the car in and out of the shop, and replaced all those things and more. He kept excellent records. He did not mention this problem to me, but I knew 'something' would be wrong because of the price so I was not surprised. The car died 3 times on my drive home, and would only restart after fifteen minutes or so. The third time I pulled a spark plug and checked for spark. None. I queried my network of mechanic buddies for suggestions. It turned out to be the pickup coil, a little gadget inside the distributor. Still running strong 5 years later.