I own a 1991 volvo 740 turbo.

The problem. The engine stalls unpredictably while idling or at any speed. It makes do difference if I am accelerating or decelerating. There is no correlation with heat or other weather conditions. The problems could present itself 3 times a day or disappear for a month. (usually though, 2-3 times a month) The engine has been tuned, fuel filter replaced, crank angle sensor replaced, fuel filter relay replaced, isolation relay replaced. Because the engine quits abruptly with absolutely no warning, coughing, etc., I feel it must be electrical rather than any kind of blockage. Volvo and other mechanics have so far failed utterly.

Does anyone have a clue?

On yo9ur 91 740 turbo there are two radio suppression relays- one mounted on each shock tower. Remove them and remove the silicon seal. Remove the case on each one and resolder the circuit boards. The solder has a tendency to crack around some of the connections- visible with a magnifying glass. Just spend a few minutes resoldering them and then reseal the case with some silicone caulk. While you are at it remove the fuel pump relay from the tray under the ashtray and give it the same treatment (without the silicone). If I remember correctly it is on the left in the second row. Bad connections in any one of these relays can result in the behavior your car is displaying.

Randy Starkie

I encountered the same problems as yours with my '91 740 sedan...diagnosis by a volvo mechanic came out that my rpm(crank) sensor and ignition module were faulty, once these parts were replaced, the problem was fixed. Since the crank sensor of yours was replaced, check or replace your ignition module.

Thanks Ric. The ignition module has not been replaced and if it's purpose is relected in it's name, it just might be the solution.

You're welcome!...I do hope replacing the ignition module will also solve your car problem, give us an update...Again, you're welcome.