A few weeks ago I posted about a problem that I was having at WOT, well after a new TPS and fuel filter the 'ol Blazer is running like it should. Thanks to all who offered up thier ideas. BTW as I was playing around under the hood, I noticed that the air filter housing didin't have any vacuum lines running towards it....intresting. After a more complete look-see I noticed that the heat stove flapper valve is operated by a sensor. I called the local Chevy dealer and inquired about it. I was told that they ran this setup because of problems with vacuum lines coming lose or cracking. The most intresting part was when the tech told me that valve doesn't open up till it reached over 200 degrees. Now I may not be the sharpest knife in the drawer, but how often does the inside of the airfilter housing reach 200 degrees? After talking it over with the tech he suggusted that I remove the small spring holding the valve in the closed position, which I promptly did. Now instead of trying to breathe thru a 1" dia hole, the engine can use the entire volume of the intake hose, all of the time. So far I haven't noticed and cold weather drivability problems and now I don't have to run $1.79 gal prem fuel to keep the engine from pinging.