So, new poster here. Throwing this up before leaving for work. I have a '96 XJ, with a full drivetrain swap ('98 engine, '92 trans.). All mods done by PO. It runs fine, shifts fine, everything is good... Until I turn on the heat (or AC, or literally any position other than off). The engine bogs down big time, and has even stalled completely a handful of times. This truck has the AC removed, and I unplugged the low pressure cycling switch after reading that on other threads, did not help.

It's my first snow day in this XJ, and coming from a Mustang, it's a big upgrade. That being said, heat would certainly be nice! One odd thing to note, I have two transmission control modules on hand. Both seem to work, as far as I can tell. However, with none plugged in, the heat will work. But that's not exactly ideal.

No blown fuses, replaced relevant ones just to be safe. I drive a 60 mile round trip to work and back every day, and it's going to start getting very cold, very fast. Any help or insight would be greatly appreciated!

 

Are you saying the issue goes away completely when the TCU is unplugged? If so that is weird, the only thing I can think of that is related between the two systems is electrical. The HVAC system is vacuum actuated so the blower motor resistor should be the only thing drawing significant power. Someone with more knowledge might be able to chime in and say if those two could interfere with each other.