Performance problem

[NovaScotiaLS]

So my sister call me and tells me when she merges onto the highway the loose power, buck and studder, then go away. So I changed the spark plugs and fuel filter for her thinking it was time for a tune up (05 cobalt 2.2L auto 100600km ). I also checked to see if there were any codes and there wasn't. it did it again the other day, it seems to do it when it's been driven at least 15-20 min and under a load as it happened to me going up a steep hill. I was thinking of running some injector cleaner through it also to see if that would help. Any help would be appreciated.

 

[YelloEye]

Air filter?

 

[NovaScotiaLS]

No I overlooked the air filter someone else mentioned that too I'll check it out, thanks

 

[onedoughboy]

I would check spark plug boots. Coil pack. Ground wires on transmission by starter. And get a good scanner that has live data so you can watch the misfire count while driving.