idle problem when A/C or defrost is on

I have a 2000 2dr 4wd. nearly 100k on it. Tune-up completed several months ago (wires plugs cap rotor fuel filter and o2 sensors)

car ran fine after the tune-up. but recently the idle has become unstable. Is it normal for idle to seek up every 10 seconds or so when A/C or defrost is on? Therer is a loud click when the idle bumps up. I believe this started recently, but you know what happens when you start listening to the idle instead of the radio. Thanks

The airconditioner will cycle in defrost - sounds to me that if it cycles every ten seconds you are low on charge, not sure if that would efect the idle cycling so much.