HELP!!!...Battery short and now surging idle...

Hello. I have a stock 90 xj 4.0 I6 and i hit a good size pothole in the road. right after i hit it, my engine died and i could smell the scent of burning plastic. i pulled over and imediately popped my hood to check the wiring. i noticed what looked like arcing marks underneath the hood. The ground strap on the firewall and the ground from the - battery post to chassis burnt completely off. after i looked at it a little bit longer and confirmed that the battery clamp had grounded out on the hood. i replaced the battery ground to chassis and the block to firewall and it started. while in park, the idle would surge from 4-500 rpm to 6-700 then stabilize. and the pattern would continue every 10-15 seconds. when i shift to drive, under load, the idle surged even more from almost stalling to 800 rpm. it will run fine as long as i accellerate but when i brake, it will surge exremely bad and almost stall.

so...what could be the problem? any ideas or thoughts are welcome. besides the two ground points burning off completely, i dont see or smell any other possible burnt wires or components. The exhaust also smells more like unburnt gas and smokes a little on takeoff from a red light. everything else electrical wise is working fine

check closely around where both ground cables were run-- if they were hot enough to melt copper, they were hot enough to melt vacuum lines too. I'd look closely at the MAP sensor wires and vacuum signal (just off the braided ground strap) all the assorted stuff (relay feeds, vacuum for HVAC/cruise control, etc) immediately off the battery ground, and closely inspect the block mounting stud for the (-) cable (as the ECU and engine sensors ground there along with the battery main cable)

EDIT: forgot to mention-- fix the battery hold-down before you hit any more bumps......

...errgh..! Well, just a short note, as I cannot help your most immediate problem.., however, what I do to each and every vehicle I had/have; is to place, and secure a piece of rubber on top of the battery, i.e., carved up measured piece of mud-flap, innertube, anything flexible, and insulative! Sure helps when I am messing around with tools laying about, knee caps, lol, etc., from shorting against the top posts. Once was enough in life, and I was lucky that I did not get a face full of an exploding, venting cell of acid!!!!! That plume went straight up and visable for around eight feet, until I managed to end the short with a handy stick! Safety first! Friend rolled his Dodge truck, from icy conditions, but batt. was secured well, but anyway stuff happens.., try to minimize them, lol.

Actually I reuse the old radiator hose for a cable clamp cover / insulator!!!

Check the wiring to the O2 sensor. It has a ground wire and 12 volt wire to the O2 sensor heater. Sometimes the wire set gets hung up in the drive shaft and causes a huge short. Then the O2 sensor gets too cold at idle and makes the idle wander badly.