Today I had my lower intake manifold gasket replaced at a local shop. Coolant was leaking internally. Anyways I drove it around and noticed it would keep at around 1600 rpm and hold a speed without touching the gas. After a while the SES light came on and the idle became loopy. I looked under the hood and noticed hissing near the throttle body. I can't really feel any air coming out of the hoses around there so what else do you think it could come from?

Check the vacuum lines.


Then take it back and enlarge the shops' posterior.

Haha, I think i'll push em for a free tranny flush.

You have a vacuum leak. Want to prove it to them? Take some carb cleaner with you, and spray it around that area while idling. When you hear the idle change, you found the leak.

When I did my UIM/LIM repair, I left one vacuum line detached from the throttle body and got exactly the symptoms you have. Once I hooked it back up it ran perfectly.