I have trouble code P0302. I already checked spark plugs they were good. The car at low speeds is putt putt putt. What can it be

The iac valve is part of the throttle body

Customer recently changed coil pack

Must be the 2.2L .... You say "Customer" .. You must be working in a shop...or sort of... OK... IF the misfire can be duplicated in the service bay, (?) then remove the coil cover assembly and the spark plug boots .. use regular plug wires hooked to the coil terminals then to spark spark plugs so the cover can be laid aside and the engine will still operate normally.. Then testing ignition fire becomes a hell of a lot easier! .. Just like checking a misfire on an engine that is equipped with .... 'Plug wires' ... NOW, if the misfire does NOT show up with the plug wire setup... Strongly suspect coil cover is cracked or circuit is failing and is leaking spark to ground when cover is installed on the engine.. May not even see a crack.. Misfire may be intermittent.. Keep in mind the 'customer' usually knows very little about auto repair.. Good luck! ....... (Rubik) .. That screen names seems mighty familiar! .. We don't mind helping out but you need to take heed of and appreciate the valuable information you get here!! .. Whether 'you' can put it to use or not depends on your skill level... Peace out!

Thanks