Hello,
This morning on my way to work, as I drove, the check engine light show up and disappear, as the check engine light shows up, the engine seemed "hesitate" and the speed drop a little but came right back. It happens 3-4 times during a 15-minute drive. Can anyone think of any cause to this?
thanks,
Cheng

Bad ignition switches can do this too. Try driving with JUST the ignition key in the slot. If you have alot of other stuff hanging on your key ring take it off.

When mine hesitated like that a couple of years ago..it was a bad coil wire. Easy fix...
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'95 854T 140,000

Thanks, do you have a link to the procedure of replacing the coil?

The coil wire is the center black wire going from the distributer to the coil, which is on the car's fender close to the battery. If your engine mount is failing, the one on the passenger side, that can cause the coil wire to move. Just check both ends of the wire and make sure it is snug.
If the fuel pump is starting to fail, first replace the fuel filter which is cheap and easy to do. Procedures are on http://volvospeed.com/maintenance.shtml
Because if the filter is clogged, the pump will have to work harder and may over heat.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

Your 850 has an onboard diagnostic box, just behind the windshield washer bottle on the passenger side. All of the codes are stored there, so learn how to get the codes and clear them.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

Thanks. But the CEL does not stay, will I still get the code?

yes
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

I finally got to it today. I did the diagnosis but both A1 and A2 come back clean (1-1-1). And the situation gets worse that I had to drive another car to work today. Any idea?

Cheng, I had a similar problem a few weeks back and it got worse for a couple of weeks, until I was unable to satart the car. I checked for pressure at the fuel rail and there was none. So I checked the fuel pump relay and it was Ok. The fuel pump was bad. It is my second fuel pump failure. First was at 87k miles, second now at 182k miles. I figured that the pump pressure and flow will fluctuate as it approaches the death, which explains the sudden and occasional power losses. And yes, my check engine also came on, but stayed on. The code was 231, perhaps because of the fluctuations on pressure and flow. Everything back to normal after I replaced the pump (OEM). By the way, mileage had been deteriorating. Back to normal now.