Like so many others, I thought I had fixed this. My 1996 N/A 850 wagon, 160K miles, was stalling occasionally, usually while slowing down for a stop or turn. This was usually preceded by some lurching.

The plugs and wires were just a couple months old. I put in a new distributor cap and rotor, and changed the fuel filter. Acting on recommendations here, I threw in a new fuel pump relay and a different fuel pump that delivered considerably more pressure at the rail. None of which stopped the problem. So I installed a different camshaft position sensor, plus cleaned the air intake (though I didn't remove it) and cleaned the MAF element. For a few months the problem disappeared.

Only to return now. Every now and then the RPMs seem to dip, the upshift light comes on, then the car dies. After cranking it two or three times it starts and runs fine.

I cleaned out the air intake again, though really there wasn't much of anything to clean out. Based on recommendations here and in the eyeball-busting, 20-page thread on this subject at Matthew's Volvo site, I'm thinking I could get a new Engine Coolant Temperature sensor and a new Throttle Position Sensor. At least they're cheap. Seems like a Crankshaft Position Sensor might be another possible solution. But believe me, any informed opinions are welcome.

The only code the car throws is P0410 — that other classic 850 problem of the air pump being dead. I've been planning to take that on once it warms up here in Minnesota. I've had that code even during the period when the car ran fine, so I tend to believe (maybe incorrectly) that the root of the problem is elsewhere. Also, there's a short on the #15 circuit (interior lights, etc.) that blows a fuse after the car is driven a few miles. But same as above: that's been true for the past year.

 

Look real hard for a vacuum leak, especially around the idle control valve. I had a 740 that use to try to stall when I came to a stop and it was usually a hole in the MAF tube, the back side of it. Also the throttle body would get a little gummed up and stick a little when it was suppose to switch to the idle side (other than the throttle cable side), so cleaning it would solve it.

Also, the P0410 is usually solved with replacing split vacuum lines.

 

What about the pvc system?

 

RSPI — so I took an extra close look around the idle air control and found a rubber connector that was worn through, which I then replaced. Thanks for the tip. I'm crossing my fingers now that this is the problem. The vexing thing about this stall situation is that it comes and goes. I've thought several times before that I had it licked, only to have the car stall on the next trip to the grocery store.

MattyXXL — thanks, too, for your suggestion. I don't have the classic smoke-from-the-dipstick-tube symptoms, so I'm not sure whether it's worth trying to go anywhere with that.