92 Pontiac timing?

This question involves a 1992 Pontiac Grand Prix LE, 150,000 miles, and has the 3.1 engine, automatic transmission

A little history =The car surged real bad on some days but not others. Can't be tied to temperature or speed or engine RPM's. Then it started popping through the intake and exaust, but only on the days it surged and bucked real bad. Other days it runs like a top. Check engine light never came on and no codes in the ecm. I was going to give it a set of plugs and wires this week end but last night it started and ran fine, drove 30 miles at 55 mph and ran perfect. We went inside to eat and it started right up when we came out but when I put it in gear it died. Then when I tried to start it all I got was popping and backfireing. I did this several times and finally ran my battery down. I left it for dead 30 miles from home. Today I go back and see if it would start, and it did. Idles fine and even revs fine, then dies when I put it in gear. Then I tried to re start it and it popped from the intake end and backfired out the tail pipe. I am confused as to why it runs good one day and terrible the next? Now it still runs smooth but dies when you put it in gear. Where do I go from here? It only seems to back fire and pop through the intake when I have to re start it several times. If I leave it sit for several hours and try to start it it doesn't pop and back fire, but dies when I put it in gear.

Thanks in advance