Won't run with heater on

I have a 96 xj. Started it up yesterday to drive in town and let the heater on defrost. Went to go back out to take off and it died as soon as I put it in a forward gear. I'd put it back in park and try to take off and it would do it again. But as soon as I turned the heater off I could drive it all day long. Don't have a clue what's going on. Any ideas?

maybe a dirty iac. its supposed to open when defrost or a/c is selected. it allows for more load from the a/c compressor.

once you put it in drive or reverse it will add even more load and cause it to stall.