I have a 2009 Pontiac G5 (2.2 L 4 CYL) and I've been getting the P0303 code. The first time I got it, I replaced all of the spark plugs. That seemed to work for about 2 months but recently it came back one. I swaped the coils to see if it was one of those but no dice, after a few days the P0303 came back on.

I put a lot of miles on my car (about 140 a day). After driving to work today, I get in the car to head home and engine light's off. (it has reappeared just 2 days ago and now turned off on it's own)

Not sure what's going on or how serious an issue it really is if that light goes on and off?

Any help/advice would be greatly appreciated, thanks!