Wife says car suddenly started running very rough on the way to work Friday. Check the
codes, get only "cylinder 3 misfire". OK, plugs are old anyway, so replace all four. Now get
"cylinder 3 misfire" *and* "cylinder 4 misfire". Yes, I gapped them correctly, double-
checked underhood sticker and factory service manual.

Pull plug wires. #3 wire and coil tower corroded. Replace all four plug wires, and wire-brush
#3 coil tower. Now only "cylinder 4 misfire". Engine still runs badly rough.

Coils check OK on ohmmeter, but heck, they're 18 years old, replace them anyway. No
change in rough running or in codes.

Hmm. Fuel problem? Pressure seems OK, so why is #4 misfiring? Disconnect #4 fuel
injector. Engine runs the same with or without #4 connected. Voltage is present at all four
injector connectors.

Removed fuel rail, replaced #4 injector, reinstalled fuel rail.

Now it won't start at all. Cranks OK, and sounds like it's almost catching, but it doesn't run.
No codes, either.

Service manual points at crankshaft position sensor or stuck EGR valve as possible
causes. Pulled sensor, checks out OK (measures 778 ohms, spec is 700 to 900). Pulled
EGR valve, not stuck.

And at this point I am baffled. Any ideas?