A couple of years ago my 1994 Volvo 850 wagon began to stall very infrequently. Almost every time, it stalled after shifting from park to reverse and applying a tiny amount of gas to back out of a parking space. I learned that if I tried to restart immediately, it would not start, but if I waited for 90 seconds, it would start without a problem. This went on for two years until, one day while driving 30 MPH down the main street in my town, it cut out. Over the past few months it has stalled while underway several times, always restarting after a 90 second wait. The last time I drove it, however, it stalled twice while underway and, the second time, it took close to 5 minutes to restart. I fear I am losing it. Workshops will not work on it unless they can see what’s wrong with it, and it doesn’t happen frequently enough for them to see it, so I am at a loss as to what to do. Any ideas?
Now that you can get it to not start for an extended period, you can do a little troubleshooting of your own. Carry a spare spark plug and a can of starting fluid. When the engine will not start, pull off one of the spark plug wires; connect the spare spark plug; lay it on the engine; crank the engine; and see if you have a spark. If there is a spark, reconnect the spark cable; squirt a shot of starting fluid into the throttle body; and see if the engine runs until the starting fluid is used up.
Get back to your mechanic or us with the results of this troubleshooting and we can go from there. Hope to help.