Bad spark plugs (remove, check now. Copper = 15,000 mile item, iridium = 100,000 mile item, platinum = misfires, bosch, champion, e3=misfires)
Massive vacuum leak - check all hosing, especially on passenger side of lower intake manifold
Clogged cat (this bad, you'd totally notice the rotten egg smell) (150,000+ mile item)
Dirty Mass Airflow Sensor - just clean this with CRC mass airflow sensor cleaner
Gummed-up throttlebody - just clean this with throttlebody cleaner. Toothbrush might help.
Intake filter clogged with leaves (30,000 mile item anyway)
Clogged fuel filter (30,000 mile item anyway)
Clogged/broken fuel injectors
