2002 rough idle and CELs
 

2002 LX 2.3 L, 5-spd., intermittent rough idle when warm for 3-4 years.
CELs -all misfire codes: random, cylinders 1 & 3, sometimes cylinders 2 &4; codes come and go

The usual suspects have been replaced or eliminated: Plugs, plug wires, fuel injectors, valves adjusted, etc. I'm wondering if it could be the IAC even though I never have had any related CEL codes. Is it possible for the IAC to cause misfire codes? The car runs fine except a rough idle intermittently but only when warm.

Which things have actually been replaced? For the ones "eliminated", how did you test to eliminate them from suspicion?

What brand of spark plugs are in there now?

You didn't mention the distributor cap. Have you checked for arcing across the surface of the cap? For that matter arcing or insulation-breakdown in the plug wires?

I was thinking the same thing about the cap and rotor. But what plugs did you install? Denso or NGK? Those are the preferred plugs for Hondas and Toyotas.

Thanks for the responses! Plugs are NGK. Plug wires replaced twice, replaced dist cap and rotor, later entire distributor with new cap, valves adjusted twice. Switched cyl. 1 and cyl 4 injectors because P0301 always shows up first, no change, EGR valve & IAC cleaned.

I checked records, this started in 2012. Misfire codes from the beginning. Except:

Old codes:
5/13: P1456 - gas cap replaced.
4/18: P0133 (O2 sensor) once only never again.
6/18: P1607 (ECM/PCM) once only " " .

I'm very tempted to replace the ECM next.