Rough idle problem with blower motor malfunction

[Rod Knee]

I’m having a strange issue with my xj. Six weeks ago frame stiffeners were welded to the jeep at local shop. A rough idle was immediately noticed. A mechanic I took the vehicle to corrected a vacuum leak and I thought the problem had been rectified. Then while offroading, the idling problem reoccurred and blower stopped working simultaneously once it started raining. I have hood louvers.
The strange thing is the rough idle only occurs when the vehicle is in D and the switch for the blower motor for a/c and heat in the cab is not on the off position. The vehicle stalls in this situation when braking for a stop sign. I can make this problem disappear by turning the air conditioning/heater/defrost/vent switch to the off position.
Anybody had a similar experience? From my understanding the blower motor and idle control have nothing to do with each other. The throttle body is clean and so is the IAC sensor. I replaced the blower motor and resistor yesterday. Maybe the welding on of the frame stiffeners resulted in a wiring problem (?). The problem occurs immediately upon starting the vehicle when cold so I'm thinking its not heat soak effecting the injectors.
Any ideas?

1996 xj, automatic transmission, 4L straight 6

[lawsoncl]

Check all the ground cables, especially between the body and engine at the back of the firewall, and from the bolt by the dipstick to the battery. If the welder clamped his ground to the battery or some random place on the body, he could have burnt a ground cable or connection.

[Rod Knee]

Thanks. My mechanic is going to check voltage drop in a couple days which, as I understand, could indicate a bad ground.