Fast idle on my Rendezvous on 2005 Buick Rendezvous

My 2005 rendezvous has begun to idle in excess of 2500 rpm s, whether in park or neutral. if you leave the motor running at this idle rate, the temp. gauge will go to the 3/4 mark for a little bit and then drop back to normal. In drive, you can reach 50mph without touching the accellerator. No dash lights ever come on and a diagnostic test revealed nothing wrong. If you turn the motor off and restart, it may be fine for a few minutes, then begin to idle fast again. Thank you

by in Rockville, IN on May 30, 2010
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2 answers 3 comments
ANSWER by , May 30, 2010
idle air control motor may be bad or gross vaccuum leak. take it to a shop for them to verify. Roy
COMMENT by , May 31, 2010
Thanks, Roy. I have had it to my local guy twice...when you say gross vacuum leak, would that be the intake manifold gasket?
COMMENT by , October 27, 2013
hi if you figure out what this problem is please do share my 04 is doing the same thing i have changed many parts pcv valve and the line for it cleaned mass air flow sens and idle air control sens is new nothing i change seems to help it but yes in park and n it goes up to about 2500 r 3k and you can reach about 55 without gas peddle being touched
COMMENT by , June 08, 2014
I also have a 2005 rendevous which is doing the same thing idle at 3000 rpm but the turn off and may be fine the next couple of starts mechanic put on computer and says it shows that everything is fine..... Does anyone know what to replace or how to fix this problem????
ANSWER by , September 01, 2015
My 2005 Rendezvous had the exact same issues. I did a couple of things that did not work including cleaning the throttle plate, put in new air filter, tried some gas additives. My answer was a 13 dollar part from auto zone that I replaced myself. It was the coolant temp sensor. On my vehicle it was about a 10 minute job to pull the old one and pop the new one in. Instanly fixed the issue about 2 weeks ago and havent had an issue since.