1995 Dodge Truck engine backfires under light load

If the check engine light is on, and it should be, put your key in the ignition, turn from off to on three times ending in the on position, the codes will flash, a 22 would be read as 2 flashes, a short pause, then 2 more flashes, they repeat three times. Codes 55 is the last code and denotes the end of the list! Write the codes down, and post here.

12= Battery disconnected within last 50 key-on cycles, or module power lost.
21= 02 Sensor cicuit.
37= Barometric pressure solinoid cicuit, or torque converter lockup solinoid.
55= End of diagnostic trouble codes, or IAC does not move properly.
Try checking all your connections at the module, and clean or replace battery cables, If you clean em, do both ends, especially for the neg(-) cable.