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.