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2001 Chevy Cavalier high idle problem help please

Chris544 Chris544
New User | Posts: 1 | Joined: 06/09
Posted: 06/17/09
06:05 PM

2001 Chevy Cavalier Z24.  The engine idles high while in park-about 2000 to 2300 so when I put it into gear there is a huge thunk as it goes into drive. My Mechanic says the high Idle is due to the mass air flow sensor thinking the engine needs more octane( per the check engine light code) and the thunk from the tranny is because as it goes into gear the idle is high causing the thunk.  He told me to do The following and I have ( just today) New fuel filter, fuel system cleaning and run super through the tank as opposed to regular and it should fix the problem. Does this sound right? Other then the above described issues the car runs great. Looking for an opnion please.  Thank you!


waynep712 waynep712
Enthusiast | Posts: 651 | Joined: 10/08
Posted: 06/17/09
09:34 PM

what is the coolant temp when you scan it??????   with the engine cold and then warmed up...   if the thermostat is broken open...  or removed.. gm computer programs will keep the engine at fast idle like you describe if the temp does not continue to increase above 130F ...  put in a new 192F thermostat...  look for a 9 as the last digit in the part number...   or the stamped in number on the bottom 192F 95C

look at the idle air counts...    should be 20 to 50 .. with the engine above 190F...     if the IAC counts are below 20... and the idle speed is high like you describe... look for vacuum leaks...  power brake boosters blown...  blown intake gaskets.. warped intake manifolds..

look at the throttle position sensor voltage... should be more than half a volt.. but less than one volt...

if someone has messed with the base idle setting... popping out the antitamper plug and re adjusting the throttle stop screw... it needs to be adjusted to what ever the base idle says with the air bypass plugged.. or if you have the proper idle air controller.. with it controlled closed...   base idle is 500 rpms on most engines...  if it is too low...  the throttle blades will stick when trying to open them from idle...     worn throttle shaft bores will also affect idle speeds... and turn on the check engine light for TPS... if the throttle does not return to the exact same voltage every time you close the throttle... you more than likely have worn throttle shaft blades...

what codes were set... the shop should have written them down on the receipt... other wise you could go back for the same code over and over again...  

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