02 grand prix

When i go to start the truck, it's a 00 silverado 5.3, and turn on the heat it blows cold air even though the heat is on. I usually let it warm up for 15-20 mins. and it is still ice cold air. It doesn't start to warm up until the truck is moving maybe about 5 mins. after the truck is in motion. The truck has this crazy idle where it revs up real high then the idling justs drops low like its going to stall, this goes on for a little while then when i jump in and go it doesn't do it anymore. The last thing is the security light sometimes it comes on right after i start the truck or it comes on while the truck is in motion. Any help is greatly appreciated. Thank You.

BlenderWizard

sounds like u might need a new thermostat. don't the t-stats on these trucks stay open when they break? Anyway, I used to have a car with the heat like that, but it was a result of running it with no t-stat, which is pretty much the same as running one with one that is stuck open.

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LongIslander26

Have you checked you coolant level, just to make sure? No check engine lights or anything like that?

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Vehicles:
2005 Silverado LS Crewcab 4X4
1979 GMC 4X4 Jimmy
1977 Chevrolet C20