idle problems and a batch of mishaps

ok so ive had a fluctuating idle for quite a while now so i replaced the idle air control valve, the idle mellowed out for a few days but now its back at it, im yet to touch the FITV that is on my hitlist. ALSO when i go from any gear to nuetral the idle drops to 100 or 200 RPM then recovers back to 750 or back to the fluctuation. as the idle drops i noticed my heat and lights dim out, recovering along with the idle. im sorta lost on what to check out, any suggestions?
thanks all in advance

Check your grounds,the main that you should look at is you Eli groung ontop of you thermostat house.check if its loose and clean it