Hello all. Original owner looking for help diagnosing misfire codes:
Codes: P0300, 0301, 0304, 0305, 0306, 1399.
Symptoms: Intermittent rough idle, low power, struggling up even gentle slopes at highway speeds. Runs fairly smoothly on level highway. Seems to be worse when engine cold.
Recent relevant maintenance history:
337,476 mi: new IAC
366,445 mi: new EGR valve
384,909 mi: cleaned EGR port, new valve cover gaskets, NGK plugs and coils, PCV valve,
398,744 mi: new timing belt, water pump, idlers, and tensioner (Aisin kit)
This trouble started all of a sudden.
1. I have cleared codes and swapped coils with inconsistent results.
2. Engine still runs rough and triggers codes with open exhaust (catalytic converter removed and rear O2 sensor unplugged). (Every few months was getting a low cat efficiency code so thought maybe the cat had failed.)
3. Unplugging EGR valve made no difference.
4. Measured vacuum at motor mount port. 17" @ idle, 19" @ 2000 rpm (no load)
5. All plugs pulled and inspected and looks ok. (Not something I have lots of experience with but check some spark plug pics on the internet.)
6. Verified 12v to all coils.
7. All coils have same resistance between corresponding terminals (though I have no idea the spec).
8. Disconnected battery for a bit and did the idle re-learn procedure. Still had codes come back after driving.
My mechanic took a brief look at it and couldn't find anything obvious. Said the catalytic converter was good. Also said might be running slightly lean but not sure what he based that on.
Just finished compression test tonight with cheap tester from O'Reilly. Cranked for about 3 seconds 3x/cylinder and averaged the readings.
1: 143#, 2: 154#, 3: 148#, 4: 141#, 5: 146#, 6: 160#
So at this point not sure what else to look at. The injectors are original but I wouldn't expect so many to fail at once. The O2 senors are a bit old.
Very prompt at changing oil/filter every 5000 mi and running Lucas upper cylinder lubricant and injector cleaner in tank every oil change.