i noticed when my heater is on the idles starts to surge, goes from normal idle up to like 1k then right back to normal, does it about evry 5-10sec's or so. if i switch to vent heat its fine, only in the heat and a/c selections it does this, this sound like a compressor issue or....?

 

in the wiring, line 346? 348? is the AC demand line, and might not be working, or its working, but not smoothly - it could be the ISC is a little gummy and its 'sticking' - not responding quickly enuf