Injector problems??

2000 (or so) Cavalier 2.2 has 25k miles on it. Driven maybe 10 miles per week. Ran fine about 10 days ago. Sounded and felt like a vacuum leak but after checking things out now am leaning towards clogged injectors. AZ is tough on gas and since it sits most of the time...Code was simply P0300, which just tells me it's running like crap. i put a bottle of injector cleaner in it, still no help. When I pulled the plugs # 2,3 and 4 looked rich and #1 looked really lean. Backfires at around 3k rpm and shuts down. Any ideas would be appreciated. I havn't wrenched on injection before, how would I check to see if #1 is clogged???


Thanks in advance...