this is my first time but i am trying to find out what is wrong with my girlfriends blazer,the problem is kinda high idle1000-1200,and when we shut it off it kinda shakes then it make a sound like it is letting air out the motor has a k&n air filter.parts i have replaced the egr valve,map sensor,cam pos.sensor,plugs and wires.

 

Have you checked for a vacuum leak?
Also make sure your ah hell i forget the name of it now, located in the intake and tells the puter how mauch your sucking in. K&N oil on the filter tends to leave oil deposits on this sensor which screws with the idle and overall engine peroformance.

 

I fouled mine with K&N filter oil once. Spray you mass air flow sensor down with "mass air flow sensor cleaning solution" It comes in an aerosol can for pretty cheap. Just don't touch it... Short of that, Id say vacuum leak. Listen carefully under the hood for a hissing sound and track it down. I had this problem once after I changed my cap and rotor. Turns out I forgot to put the vacuum line back on back there that actuates the A/C selector switch.