[Rwillia4]

If is is not a vacuum leak...
I would check the O2 sensors. If you ran low lead gas or other funny additives you can trash the O2 sensors quickly which are a major player in the correct fuel/air ratio. When they are bad the idle is typically the first thing to go, by not staying steady and progressively surging more. When bad they usually make the engine run rich, which could cause the backfiring (but there needs to be "spare" oxygen getting in to cause ignition). I think you maybe chasing more then one problem as previously stated.