Check that the idle control valve is clear and not gunked up.
I had a problem with my AC which would stall the engine but mine was bodged by someone previous to me. It seems like the high pressure switch didn't work and hence they'd wired it such that when the compressor kicked in, it would also activate the cooling fan. The comboned load by the alternator and AC compressor would bog the engine down so much that sometimes it would cut out.
David.