IT sounds like your car is on the verge of needing a tune up. Also bad gas or low quality gas sounds like a long shot but... When your car is 10 years old people often forget to replace common parts like your fuel filter, distributor cap, distributor rotor, spark plugs and spark plug cables. I had the same thing happen with an older toyota and it turned out to be that all those parts needed to be replaced. I replaced the worst first and that fixed the problem but with in a year all the others started to go and I had to replaced them all (it was a beater car so I didn't care). One or all of those parts could be at 80% and cause your car to notice when it gets bad gas or bad weather even like humidity (for the distributor cap and rotor).