I have noticed a noise I could best describe as an air sucking noise coming from the back of the engine as best I can tell anyway when traveling at various speeds mostly highway speeds to be exact. I can be going 70 and step on the pedal and it almost sounds like a grinding or vibration coming from the engine not in the drivetrain (U-joints). I let off and get back into it and it seems fine but that damn sucking noise is still there. I cleaned th TB along with th IAC. Installed everything back onto the engine. Still the same results. Also seems to me to be a lack of quick acceleration and the gas mileage seems to be kind of crappy. I just purchased the truck and it has 113k on it, seems to idle fine just sitting but I notice in drive I can slightly let off the brake and it kind of shakes but I have not noticed a drop in RPMs on the tach. No check engine light, it's not using oil, idle stays steady unlike a failed TPS would indicate. I have not noticed any vacuum lines damaged either. Just scratching my head on this one. O2 Sensor maybe? IAC going bad? Any suggestions? One thing I have not done was throw the scanner on it.

 

Check for a blown plenum gasket

 

I actually meant to check that when I had the TB off. I will pop off the air intake and take a peek down in there, only thing is it is not using oil not that have noticed anyway but it definitely is a possible symptom of a blown plenum gasket.