On a friends Volvo wagon w/ about 300K Miles. The car is in excellant condition:

Usually the engine runs fine, but very occasionally (1 to 3 / week) it suddenly just ceases to produce all power.

This has happened:

On wet and dry days, in hot or sub freezing weather.
On the highway or in city traffic or while stopped.
With gas tank near full or empty. Drygas does not help.

There is no sputtering or indication a failure is imminent. The engine just stops firing. So far, it's always been possible to coast to a safe stop.

After a failure, if the key is turned off and then immediately turned on again, the engine starts and runs without problems.

Any suggestions would be most welcome.

Thanks.