2012 Equinox Stalling

Its recently been running rough on start up. When I'm idling it starts to sputter or when I put in reverse it'll completely stall. It's giving me a p0300, which it has done since I got it 2 months ago but that code randomly comes on and off. Ive changed the spark plugs which caused the check engine to go off for about 3 weeks and it came back on last week.

On Wednesday i changed the air filter & intake solenoid but no luck. I was thinking the fuel filter but that looks like it'll involve dropping the tank. The only code that keeps showing is the p0300. There's 121,000 and some change miles on it. The oil is showing about 70%, which I'm going to get changed today. I also cleaned out the intake manifold the best I could without taking it completely out, any suggestions would be great.