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Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 16893
Experience:  15 years GM master tech
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2001 malibu: v6..runs great..a real high idle like..throttle body..rpm

Customer Question

I have a 2001 malibu v6, runs great but recently started going into a real high idle like you are giving it gas. when it does this the throttle body is completely closed and there is no gas being given to it at the time.. when it does this it will go into an idle of about 3200 rpm or more sometime. its like you are pressing the gas but your not and i have checked the throttle while it is doing this and it is completely closed and retracted like it should be.. when it does this you can stop and cut the car off for a few minutes and cut it back on and it will idle fine but after you drive it a little it will start reving up really high again..
Submitted: 8 years ago.
Category: Chevy
Expert:  lazydog76 replied 8 years ago.

hi, have you checked the iac valve, it controls the idle and could cause the unstable idle. the iac is controled by the pcm. the valve is located on the throttlebody.

also be sure to check the engine for a vacuum leak at the intake and throttle body.

Customer: replied 8 years ago.
No sir I have"nt checked the iac valve, not really sure where that is on the throttle body.. but like i was saying it runs great 99% of the time. it idles real smooth and normal like it should and then all of a sudden it will go into that really high idle and it wont quit til you cut the car off and restart, then its as smooth as silk for a while till it does the same again.. I have seen it idle at almost 3500 rpm a couple times .. so would the iac have something to do with that. already checked for vacuum leaks that was the 1st thing I though of.. I am so puzzled with this.
Expert:  lazydog76 replied 8 years ago.
yes, the pcm controls the idle by using the iac valve, this valve opens and closes to obtain maximun and minium idle. the iac can be tested by using a scan tool to make it operate by working the valve through the pcm. this will also check the pcm operation. does it have a check engine light on.
Customer: replied 8 years ago.
no sir thats what strange, no check engine light on or anything.
Expert:  lazydog76 replied 8 years ago.
ok you really need to check this with a scanner, and watch the data from the sensor
Customer: replied 8 years ago.
ok just one oone question to be sure i understand this. i was under the impression that a bad iac valve would cause stalling or rough idle, but your saying it can also cause the car to go into an extremely high idle also? correct? I mean this thing will idle so high if you go down the road you can maintain 50-60 mph without your foot even on the gas..
Expert:  lazydog76 replied 8 years ago.
ill opt out and let someone else answer........
Expert:  Gary replied 8 years ago.
i would like to help if i can...have any parts been changed?did this happen all of the sudden?or something that slowley has gotton worse?the IAC is used in place of a choke that used to be on carberators..the computer uses the IAC to make a controlled vacumm let that bypasses the throttle plates threw a port machined in the thottle body to keep the idle where the computer has been programed to put it..if the IAC opens all the way up for some reason a big vacumm leak will cause i high idle or RPM'S way too high even when driving almost like the cruise is on...let me know