93 Jeep Cherokee blowing 30 amp eng. Cont. Fuse

Hope some one can help me, My son jump started his buddies truck and as he tells it, he hooked the cables backwards on the Cherokee, he said it was just for a second and instantly the throttle body sounded differently, he drove home and drove to work the next day, on his way home it blew the 30 amp. Eng. Cont. Fuse, I changed it but it will blow it after about five mins. Of driving, it can sit and idle no problem, but as soon as I drive it it will blow.
I changed the TPS, no difference, I get code 12, checked the voltage at the battery at idle it shows 14.33volts, Doesn't change with higher RPM. The battery has been kinda suspicious for a while, corosion build up from water leaking from the top, when I look in the cells half look black and I found a small piece of rubber floating in one, The volt gauge in the cluster only shows 12 volts or less with lights on. I am leaning towards shorted cells in the battery, but I would think it would short at idle not just driving,
If any body has dealt with this or can kinda confirm my suspicion, I would really appreciate it.
Thanks in advance for any help.