98 Malibu 2.4 rough idle

Car just starterd a very rough idle one day, not gradual. Rough at 500-700 rpm. Does it when cold or warm. All sensor including O2, idle, EGR, etc have checked out ok at a repair shop. Put new plus in, new fuel filter. NO CODES. Any ideas? Would a fule regulator cause this? Thanks Rod

You may have a bad coil cover- it bolts to the underside of the top plate and acts as the spark plug wires. Remember to use OEM plugs with this setup-DO NOT CHEAP OUT!!!

I replaced the coil cover and plug boots and OEM plugs. Still the same. I finally am getting a code of P0440. It may or may not be related to this problem since the code comes over 500 miles since the rough idle started. How about the fuel control valve? Can it allow too much fuel at idle? What could code P0440 be? Thanks
Rod

P0440 relates to the evaporative emissions control system. Check for bad hoses to the canister. Could also be a bad fuel filler cap.

Check For any vaccum air leaks

Thanks for the suggestion. I have searched for the vacuum leak and can not find it, however it was a frustrating day so I will give it a go on a fesh day.
Thanks for you help, will update status later.
Rod