when you changed your plugs,,, check for internal broken wire,
check coil pac some times the wire gets loose when removed and put back
also sounds like a vacuum leak under and near the throttle body,
, look in the throttle body if it is black, clean it it may fix your problem
put two bottles of injector cleaner drive 60 to 100 miles
then put one bottle every 5 to 7th tank full OF GAS