Heat only comes on once in a while on my 1991 camaro

Question edited for clarity.
Question moved to model category.

Diagrams in the link

https://www.google.com/search?q=1991+Chevy+Camaro+RS+V8.+I+need+vacuum+line+schematic

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I don't know about the older panels, but on newer ones, remove the IP, turn it clockwise and let the needle come around to 0 Plug it back in and check before you reassemble. if it doesn't work replace the TAC electric motor.

replace heater blower fan

time for a trip to the salvage yard or to the dealer will cost 200 salvage cost is like 20-40 for switch

Hi,
My name is Chuck and I'd like to help you figure this out. The smell you have,is it a sweat smell? When you turn on the defroster,does steam form on the inside on the glass?Have you noticed the cooling system level going down? Or is the floor wet on the passenger side?If you are experiencing any or all of this,you have a leaking heater core.
Let me know if this is what you are experiencing and if you want information on how to replace it. Thanks,Chuck

You may have received the wrong sensor or a faulty one

bad spark plug wires sounds like or fuel injectors

vauum leak is what is goin on. you need to make sure vacuum line going in for vent controls is not cracked or broken under the hood before it goes in to controls. hopefully it is on the outside andnot under dash

I see this was asked years ago but never answered. So for the future questions about this,
The doors and roof panels on 4th Gen F-bodies are SMC (Sheet Molded Compound), a form of fiberglass. The skin is glued on. To remove a glued on panel use either a heat gun or a plumbers torch (Map Gas). Heating around the skin where the panel is bonded to the inner structure will break down the adhesive. Be careful not to burn the SMC away in a fire (heat guns are safer than the torch). Where you start, insert a putty knife to lightly pry the skin off as you heat the area.