I have a 1994 Infiniti G20 that is misfiring and has a rough idle, but does not trigger any codes. I have done the following: new plugs, replaced fuel filter, replaced air filter, and changed the valve cover and spark plugs seals. It doesn’t misfire every day, but when it does it does it constantly. Any ideas?
Your vehicle has the OBDI engine management system. OBDI doesn’t monitor for engine misfires so the check engine light won’t come on if one occurs.
When was the last time the secondary ignition system was serviced? This includes the distributor cap, rotor, spark plug wires, and spark plugs. If you can’t remember or don’t know if these have ever been replaced, it’s a good place to start.
I have not replaced the cap, rotor or wires. I only replaced the plugs when replacing the valve gasket cover. The misfire only happens occasionally (every few days), so if the cap, rotor or wires were bad wouldn’t the problem happen all of the time?
Now, concentrate on a possible fuel supply (pressure, delivery, and injector spray) problem. Change the fuel filter, and check the fuel pressure statically and with the engine at idle, at higher rpm, and under load.
The short answer is “No”. It would not happen all the time. The amount of humidity can effect this. If you have a distributor and spark plug wires on a 94 anything, and you don’t know when they were replaced, then replace them. No point in further discussion. Do it.