2wd-K5

alright, it happened right after the warranty ended, and it seems to be getting worse, when the a/c is on the engine idles funny dropping to 500 rpm then jumping to 1200 rpm up and down up and down at an idle, it smooths out after a minute or 2 if i take it out of gear. now it seems to do it without the a/c on i had the heat on this morning and it did it again. i wouldnt have noticed it as much if it werent for the heater fan dropping in speed as it is doing this. i dont want to spend any cash if i dont have to, i will be trading it in for a trailblazer soon. any thoughts?