Run rough, shuts off, backfire

Car ran great. Stopped by friends house. Went to leave would not start. Gas needle does not work so thought low on gas although should not be. Used starter fluid to check. Car started. Went to go to gas station and died pulling from stop sign like out of gas. Got gas. Would not start. Used starter fluid. Had to drive two feet to keep running. Later evening could not keep running. Shut off when put in gear. Runs rough and have to baby sit pedal. Backfires through intake and exhaust like bad miss. Problem is intermittent. Sometimes runs at idle just fine. Can rev up slowly to 3,000 rpm and let off slowly. If revved quickly it want to shut off like fuel saturation or no air. Have checked air filter and working on without air filter and changes nothing. Inspected plug wires, cleaned plugs and changed coil packs. Sometime start and idles fine but revs quickly wants to shut off. Sometimes start and runs like crap and have to babysit pedal.
In working on have found a missing exhaust manifold bolt on far right cylinder on drivers and loose bolt on bottom of same. Can hear a psssss sound from back side of engine but do not know if that is new or not. Not a very loud one, very faint if not listening for may not notice.
Now showing number four misfire, O2 code and a class 2 ground (will include picture) when before it was only showing low fuel on acceleration code.
When run rough it backfires through intake regularly and through exhaust like really bad miss. When idles good and revs up slowly no problem but when let off gas quickly it backfired through exhaust, again like bad misfire.
At one point tried to put in gear and shut off. Now transmission stuck in park and ignition switch will not turn to off position. Anti theft light comes on when switch turned to on position but goes off like normal.
Have been told could be fuel filter or pump but cannot see how filter or pump could cause backfire through intake. Thought about timing but timing does not fix itself part time. Have been told could be ECM but in my limited experience when an ECM goes it is done, again no part time. I have not pulled valve cover yet to check for broken valve spring which I have been told can work intermittent depending on where or how it is broke.
Only car we have and do not have money for down payment on another or credit to keep from getting ripped off due no my medical bills. Help!
The P1171 code was showing already as well as a fuel sensor code for the fuel level which is why the gas needle does not work!