rough idle

I've got a 2000 Ford Focus LX - non Zetec engine with 69300 miles. The engine will sputter every once in a while when at idle, and only after being warmed up. I've replaced the plugs, plug wires, fuel filter, O2 sensor, pcv valve, and I never buy the cheap gas (chevron or shell only), and i've even used a couple of bottles of the Valvoline fuel injector cleaner. My check engine light has never come on, but the sputters are so bad, that you would think the engine is going to stall, but it catches itself everytime.

Any ideas?

Sometimes the RPM's are set to high and can give you a rough idle

Thanks for replying. Actually, it was dirty injectors. Got them cleaned, and the engine works like new again.

Glad to be of help.