I'm having trouble on where to start looking for this problem. Friday on my way home from work as I accelerated air stopped coming from the vents and instead started coming out the floor and defrost vents. When I slowed down (of course the RPMs going down) the air started coming back out the vents again. When I sped up (RPMs going up) the air stopped and again out the defrost and floor vents.

I'm pretty sure I have a vacuum problem, but doesn't this normally work the other way around? On another car I used to own (92 Grand Prix) air would only come out of the vents when the RPMs were high, which makes sense since there would be more vacuum.

Today it started to do that again but after a while corrected itself and stayed normal the rest of the drive.

Any ideas on what's going on?

Thanks for any advice. This site has been an invaluable resource and I've solved many issues I've had with my firebird with a simple search here. I can't express how awesome this site and the community are.

 

Remember the highest vacuum is at idle. As you open the throttle the vacuum declines. So yes you are losing vacuum somewhere.

 

Thanks for clarifying man. I'm thinking it's at the switch since I can hear a hissing noise from it. Figures this would happen in the heat of summer.