94 jeep codes 12,21,54,55, light comes on but once you restart it , it goes out until it comes on again, . could it be a small leak in the intake system

This is the info I have on codes--

Code 12: Direct battery input to PCM was disconnected within the last 50 key-on cycles.

21: Neither rich nor lean condition detected from the oxygen sensor input.

54: No fuel sync (camshaft signal) detected during engine cranking.

55: Completion of diagnostic trouble code display on the malfunction indicator lamp (check engine lamp).

Code 21 sounds like a bad O2 sensor, 54 a bad cam sensor.