So while I am driving my truck, I hear a hissing noise coming from the engine. This occurs when I let off the gas and goes away in about 5 seconds. If I press on the gas and let off, but I don't completely let off, the hissing noise will stay until I let off the gas completely or press even more on the gas. I just want some thoughts on what this is. If it's my intake working properly or improperly. Also if it is some thing I should worry about.

 

Your probably just hearing the air being drawn through the IAC (idle air control) on the throttle body. Have you ever removed the throttle body and given it a good cleaning, especially around the IAC ?. If not it would be a good idea because they can get pretty dirty. You will need a new throttle body gasket.

 

Thanks for the thoughts! I'll be sure to check that out as soon as I can.

 

i was gonna guess the throttle body bolts need a little extra torque on them, but who knows maybe the gasket ripped.

 

Three times I have heard hissing:
1) When a shop didn't re-install the air hat properly
2) When a O2 sensor was going and it idled and loped weird on startup
3) After installing the 14x3 eddy cleaner I hear it until it warms up (kind of like a turbo)