okay, so i have a 2004 GMC Sierra 1500. Just last week it started ramdomly dropping RPM's. Sometimes it does it when I go to pull out of a parking lot and also when it is in park at an idle. I've replaced all the spark plugs. But that didn't fix the problem. Can anyone tell me how I can fix this? On another note, for awhile now my heat has randomly started coming on, even with the AC on full blast it blows hot air out of the driver side vents. It just ramdomly chooses to do this and I haven't found the cause. If anyone knows how to fix this I could really use some help. Especially with the temperture getting up to 110 degrees F where I live. Thanks

 

the a/c is most likely the left temperature actuator...but it really needs to be scanned to know for sure..
The idle...could be a bad idle valve..OR..gm has an update software flash to fix soime low idle concerns