The following happened during a trip to California from Illinois - via I80.

Car was moving along great for 2 days, but very suddenly started to lose power while taking a hill in Nevada. Check engine came on (flashing). Stopped at a summit parking area. Engine idles very roughly but has some power at speed (but less than normal). Car was able to move so we progressed to the next town to check things out.

Codes - 6 codes set, all related to misfire on multiple cylinders. Reset codes and a different set (also all related to misfires) came on. Check engine light returned, sometimes steady sometimes flashing.

What I did so far:

replaced spark plugs which were worn and very white (evidently indicating a very lean fuel mixture). Distributor cap and rotor are a bit worn but - this problem came on very suddenly.

verified fuel pressure - fluctuates some but near 40 pounds. Fuel pressure increases properly if vacuum line to regulator is closed off. Fuel filter is about 40-50000 miles old.

cleaned out throttle bore - inspected all sources of possible vacuum leaks I could find - everything seemed tight. PCV and flame trap are not obstructed or leaky that I can tell.

checked MAF sensor and idle air control by disconnecting them. If MAF sensor is disconnected (which should cause fuel delivery to be constant) the engine surges at idle, rather than running smooth. This suggests to me the fuel mixture is very lean. If IAC is disonnnected idle slows down lots as expected.

No obvious signs of mechanical problems in engine - oil consumption did not increase, nor are oil and coolant mixed or contaminated. No new noises or knocks, no sign of overheating.

The problem did not seem to get worse, so we progressed on to our destination in California - where we can check things out more carefully.

My hypothesis is I got some bad fuel or some dirt got dislodged and something is clogging the injectors - haven't looked yet.

If anyone has further ideas on this, I hope you'll share them.

Thanks to both of you -

The car sure does act like it has a huge air leak or is very badly starved of fuel or both. Can't find any sign of leak so far. I can't tell if the engine runs better before warming up - weather is quite hot now and the warmup is pretty quick. It starts easily.

I too suspected poor fuel. There was no issue though until suddenly at which time I had gone thru about half of the most recent fillup (which was 85 octane). Before that I had run the tank to near empty. Once the problem occurred I did top up with some 91 octane and things certainly didn't get worse - maybe a bit better but very far from right.

I guess the best plan might be to remove and inspect the fuel injectors.

Probably too late now, but the tube from the air cleaner to the throttle body may be cracked. Or one of the vacuum elbows at the manifold.

I doubt that the fuel filter let through any garbage to plug up the injectors. So check the injector wiring instead.

Klaus
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I still miss my 164

Thanks Klaus - I did replace that bellows which had cracked - a couple of years back. Symptoms were similar but very mild compared with this.

Regarding the fuel, the possibility is heavy deposits of organic material that went through the filter (because they were dispersed) then congealed on the injectors.

Wiring is also a key point which I will check.

Maybe an intake maniflod leak. Does it run better for a while when it's cold?

Poor car :)
It probably got some 85 octane that they use out west with a large dose of ethanol in it. Unfortunately, the ethanol likes to collect water and if the station is not busy...
I would buy some good premium gas at your next station and see if that helps. The flashing CEL is because of the "damage" to the cat message, ignore it.
You will always loose power at altitude, the air being much thinner especially on hot days. My V70R didn't want to "go" in Colorado Springs at about 6500 feet.
Clear the codes when you get back to sea level. If you are fully loaded, try shifting down to 3rd when going up long inclines, it will be better for your tranny also.

Klaus
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I still miss my 164

I had the same problem on my 96 850...had two bad spark plug wires. The boots are so deep you can't see the arc or hear them shorting but when I pulled the wires there were scorch marks. car ran like a clock after I changed them

i had plug wires die on an old 8 cylinder chevy (sorry for chevy-ing up the place). sounded like a three legged horse trying to gallop. OY! like any dumb white male i just kept on goosing the gas pedal to see if a good high rev would blow it out like a cough (roll eyes) it blew the danged muffler open in a backfire. so,... i got to looking under the hood. it ended up being plugs and wires.... and a muffler. (roll eyes again).

good luck and i hope you get running well soon!
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-woodsytf '95 850 wagon 160k

Thanks gentlemen,
we will inspect the wires very closely. I too had a similar problem (on a Ford). It looked for all the world like mice had eaten on the wires and replacing them (and installing with good dielectric grease) cured the issue.

ksg