On two occasions my 850 wagon (150K mi) has suddenly lost power while driving down the road, the engine becomes unresponsive, slows down until it dies (while i am coasting to a stop). At the moment the engine dies the usual lights come on in the dash. In less than a minute, I crank it and it starts and runs perfect. No Check Engine light, no stored error codes whatsoever. Independent Volvo shop in town kept it and drove it for a week, and of course, it would not do it there, they could not find anything wrong. This is bad news, because the wagon has been our "travel car", but now I do not want to risk taking it far from home like that. Any suggestions would be appreciated, what parts to procure, U Pull It or new, etc.

Carlos
'94 855 automatic
'88 244 5 speed 200k mi

Sorry, it was the mass air flow meter causing the stall not the cam sensor....easy to replace

I agree with the others that the fuel relay is a likely suspect.

I'd also caution you about depending on some old boneyard relay that has seen 15 years of
service. Relays go so many cycles before they act up and finally crap out.
I'd use the boneyard relay for troubleshooting only, and once you're certain that it's the
fault, get a new one in there. That boneyard one is certainly pretty tired.

Bill

Mine did that. The problem was a defective cam sensor. Easy fix.

AFAIK ALL Fuel pump relays are dated. MANY times you can pull a replacement one (remember they're european so DDMMYY) that's 03+ .. Then again, fcp has them for $35 so thats not too huge a mark-up...
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If you're not driving it "like its stolen," are you really driving?

How many relays will cause the 850 engine to quit?
is there a RSR relay beside the fuel relay?

It might be a good idea to replace those critical relays on a schedule.

$35 for a fuel relay is cheap money compared to all the BS that accompanies
it's failure. Murphy's law what it is, the relay will fail when you're
racing a tsunami up some hill.

Fuel pump will, and is likeliest to fail. Main relay can fail which would knock out the injectors. There's got to be a few more, but I can't think of them.

I think the two stage operation of the fuel pump relay is what leads to its early demise.
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If you're not driving it "like its stolen," are you really driving?

Carry a spare fuel pump relay.

Klaus
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Did you do your Random Act of Kindness today?

I assume you've looked at the plugs/wires to make sure they look good, correct? Have you ever replaced the fuel pump relay? That tends to go intermittently, easily obtainable at the junkyard.

First, though, I'd go with cleaning the throttle body and idle air control valve. Gunk can build up on them and as you coast down it can cause problems. Take some break cleaner and go to town on them. The IAC is the cylindrical motor forward of the throttle body with two hoses coming to it under the plastic cover.

You might want to make sure your air filter is in good shape, and perhaps its time to clean out the PCV system if its been a while. The PCV system takes ~4-5 hours to clean from start to finish if you've never done it before, you've got to take off your intake manifold (and likely replace the gasket.. order it before you start the job!). If you've got puffing of smoke out the oil dipstick you might want to think about cleaning this.
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If you're not driving it "like its stolen," are you really driving?