1999 tahoe accelerates itself

[tahoedoe]

Hey guys I have a 99 tahoe 4dr really clean body with 192k miles! Starts up right away. 5.7 btw, but it has a rough high idle in park, and then when I put it in drive it accelerates by itself, it has gotten worse and worse over a course of about 2 months. Replaced the TPS, I have a SES light that says "irregular high idle" I think it burns coolant and oil, smells like it. Could it be the intake gasket? Or head gasket? All help appreciated, thanks!

 

[tahoedoe]

OH i forgot to add, now after driving it like this for awhile, it developed a loud pulsating squeaking noise. when the idle is higher it squeaks faster...hopefully it is the intake gasket, not sure how to check? I think thats cheaper than the head gasket

 

[lesterl]

Squeak could be an idler pulley/ tensioner, water pump, alternator bearing/ etc.....

Check for vacume leaks, does the coolant get low? Oil get high?

 

[pberryny]

Have you checked the idle air control valve? Might be gunked up with carbon/soot and stuck.

 

[lesterl]

Ok, I'm game for an older post, IIRC these are notorious for carbon buildup in the throttle body also, perhaps a upper intake cleaning is also in order......

 

[hshark]

IAC or idle air control valve. This is what it seems like to me. Somebody already pointed this out so i second that opinion...

 

[tonymac617]

Head gasket = Coolant burned out the tailpipe and lots of smoke
Intake Gasket = Coolant in the oil
I tend to side on the IAC as well. Happened to my other GM vehicle.