The throttle on my 2001 Chevy Cavalier 2.2 engine stays open sometimes after running at freeway speeds for twenty minutes or more.  Getting off the freeway, the engine stays at full throttle even though I have my foot completely off the accelerator.  I end up having to turn the ignition off and settle it to a stop without power.  Very disturbing.  It goes away after sitting in the garage at night though.  Any ideas??  I took it to a garage last week and they saw what it was doing when I brought it in but when they started it up in the morning to check it out, they couldn't get it to do it again.  Frustrating.  In the meantime, it started to do it again tonight when driving on the freeway back to home.  Can anyone help?  

any chance the throttle cable if frayed in the casing???? or the cruise control is hanging up.//// try disconnecting the cruise control cable and driving it...

is it possable that the idle air control valve is hanging up...   they go wide open during cruise to act as a dash pot on deceleration.

how is the throttle shaft bore.??? worn????  you can only usually feel it when the throttle blade is partially open....

do you have a scan tool??? can you watch the throttle position sensor voltage while you operate the throttle with the engine off???  watch for glitches...      watch for it to come back to the exact voltage each time you close the throttle ...  if it varies or drifts it will mess with the ecms thinking....  keeping the IAC open....

there is one more possability  and that is a small one... that  i have only seen once.. something stuck in the throttle body blades...