The black box you are referring to is the ignition coil. If the wire connector is not snapping into position, cylinder # 2 and 3 would not function as the spark plugs would not be firing resulting in rich running conditiona and stalling.
Check for vacuum leakages of the air intake hose. The accelerator cable does not have any relatins to the problem.
The backfiring indicates somethng is wrong with the igntion timing and since the engine was running rough prior to the work, it could be possible the ignition coil packs are faulty and the work has aggravated them more causing them to fail completely.
Havethe coil pack tested or get a subsitiute pack to test.
Monday, March 7th, 2011 AT 6:51 PM