2000 Honda Civic EX

I recently had a new generic catalytic converter installed. It drove fine prior to installation. The "check eng" light was on and the code showed that the car had a faulty converter.
After installation of the converter, my car stalls in the morning as I leave for work. This creates a dangerous situation as I pull out on to a busy street with cars coming up fast behind me.
I have taken the car back twice to the mechanic who installed the converter. He not only can't find why it stalls, he can't get it to stall for him at all. Just for the record, it has stalled when my dad drives it and it has stalled with other people in the car with me. So, it is a real problem.
I took the car to another mechanic who looked the engine over and found a loose battery terminal connection. He said that when the first mechanic MIG? welded the converter on he may have disconnected the battery and then didn't connect it tightly when he was finished. He said that the loose terminal could have been fouling up the computer especially in the morning due to dampness.

Does this scenario make any sense? Is it customary to disconnect the battery before MIG welding?

I haven't driven the car enough since to know if it still stalls.

 

yes it does a loose battery ground will kill your car with no warning, the mechanic just made a honest mistake, i have done it my car before, and when i was driving down the road POOF car shut of i was like the heck. i pulled over well coasted more like it poped the hood and found the loose ground,. you should be good to go now. scary wasnt it...lol

 

The question still is: Did the first mechanic disconnect the battery in order to MIG weld the converter or install new sensors?

 

yes he did that its what your suppose to do, alot of ppl dont do it like they should.

 

Thanks! It may have been an honest mistake but it cost me over $40 to have another mechanic find his mistake.