..mmm...broken camshafts have been reported in which case the oil pump does not run anymore and only a few cylinders fire with the remaining valves blocked randomy opened thus backfires....remove valve cover and check to see if all of the rockers still move when starting....the ones at front of the engine, that is alternator side, will, but may be the rear ones (transmission side) will not..
EDIT: by the way, check these threads, dramatically showing same symptoms ; they contain several links:
http://www.automotiveforums.com/vbul...d.php?t=402930 (check the last reply..one year later, in fact following this next thread where it should have been, logically))
http://www.automotiveforums.com/vbul...d.php?t=407222