Engine Revs To 4,000 Rpm When Started

[Kyle2505]

I have a 1999 GMC sierra 1500 5.3L. Had very bad sludge and an internal coolant leak so i replaced the head gaskets and put the truck together. When i started it, it reved up to 4000 rpms and stays there. The throtle plate stays closed so i checked both the pvc hose and brake booster hose and its not coming from either. It sounds like its coming from the air filter on my cold air intake. My question is, can a bad IAC valve cause it to rev this high? I'd rather it not be a cracked intake manifold. Any thoughts or ideas are greatly appreciated! thanks

[hockeypro1411]

Sounds like a bad vacuum leak somewhere.

[Kyle2505]

Sounds like a bad vacuum leak somewhere.

 

 

That was what i was thinking. Thats why i checked the booster hose and the pvc hose for leaks. Besides a cracked intake manifold, where else could i get that big of a vacuum leak from??