When's the last time you treated it to a set of new plugs, wires, cap, rotor,
fuel filter, air filter, and PCV valve?

While messing around under the hood, did you accidentally break or knock
off any vacuum hoses?

Have you ever cleaned the IAC and inside the throttle body where the throttle
plate *almost* closes, to make sure deposits haven't clogged it so bad the
engine is struggling to breathe?

Did you recently fill up at some "cheapo" station where the gas is half water?