Crazy idle

[David01]

New to the forum...sure this has been discussed...please help...2001 1500 sport 5.2 4x4....crazy idle...sometimes high sometimes real low...idles down then cuts off...now cold or warmed up if u hit the gas it idles up high and slowly comes back down...replaced IAC-nothing...after warm up within a couple miles its at its worse...I also have the hissing/whistling noise...when you cut key off trucks turns off then acts like it turns over again then off again...help

 

[dapepper9]

Hissing is a vacuum leak, cheb the gasjet under the air hat, might have gotten dislodged or ruled out just old.

What brand isc did you use? Did you disconnect negative battery cable when you replaced it?

My suggestion is pick up the felt air hat gasket ($2),disconnect negative cable, replace gasket, reconnect battery and stsrt it see how it runs

 

[Gr8bawana]

Do you have any codes showing? My truck had similar issues with the idle going up and down when warming up. At start up it would rev up and down at about 1500-1600 rpm. Now it stays at about 1000 till it warms up and very steady idle. The same when you pressed the pedal a little it would come back down very slowly.
It was the Trottle Position Sensor. Idles perfectly now.

 

[jsmith]

Do you have any codes showing? My truck had similar issues with the idle going up and down when warming up. At start up it would rev up and down at about 1500-1600 rpm. Now it stays at about 1000 till it warms up and very steady idle. The same when you pressed the pedal a little it would come back down very slowly.
It was the Trottle Position Sensor. Idles perfectly now.

When mine acted up like this it ended up being the TPS too.