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High idle at start then dips

Tiny
MAGICBYDZN
  • MEMBER
  • 1993 GEO STORM
  • 140,000 MILES
I have a 1993 Geo Storm 1.6, 140K miles. Just got done rebuilding the motor, 99% everything under the hood is new. The car runs high at start and if I hit the gas a few times it drops back down, also I notice the IAC runs all the time, even when the car. New IAC, New MAP Sensor, New Air Temp Sensor, New just about everything else under the hood. Just cant figure out why it runs high on start.
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Wednesday, January 11th, 2012 AT 10:31 PM

17 Replies

Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
It's called high idle. Supposed to do that until the engine warms up. If it keeps up, you have something adjusted improperly.
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Wednesday, January 11th, 2012 AT 10:38 PM
Tiny
MAGICBYDZN
  • MEMBER
  • 7 POSTS
Ok, I just rebuilt a motor and everything from the ground up on this car. I've been building street rods for over 20 years, duhhhh, I know what its called and that a car needs to warm up. The engine is hot, I turn it off and then back on and the idel is high. So can someone who really knows something answer my question, please!
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Wednesday, January 11th, 2012 AT 10:51 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Only 20 years? I was in high school back then, rebuilding motors and whole cars, like my 69 Camaro. If the idle isn't coming down properly, something in the throttle linkage is probably adjusted incorrectly, like I said. Checked for vacuum leaks? Verified proper timing? Proper fuel pressure and delivery?
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Wednesday, January 11th, 2012 AT 11:24 PM
Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Unless you're perfect and never make mistakes, anything is possible. If you're perfect and never make mistakes, then maybe you were sold bad parts.
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Wednesday, January 11th, 2012 AT 11:27 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
Just to add to this one how high is the Idle?Have you checked for codes?Or vaccuum leaks?A vaccuum leak on a fuel injected car will cause a high idle if its big enough.
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Wednesday, January 11th, 2012 AT 11:36 PM
Tiny
MAGICBYDZN
  • MEMBER
  • 7 POSTS
Why would an AIC be running if the car is off?
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Wednesday, January 11th, 2012 AT 11:42 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
AIC?
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Wednesday, January 11th, 2012 AT 11:54 PM
Tiny
MAGICBYDZN
  • MEMBER
  • 7 POSTS
Oppss, IAC Valve LOL. But I went out to run it again and it ran just fine! Didn't notice I left the IAC unplugged. Seems to be an issue with the IAC, but its new and doing the same thing as the old one, clicking all the time even with the car is off. Could it be a short in the system?
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+1
Thursday, January 12th, 2012 AT 12:15 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
Could be a short do you have any codes in the computer?
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Thursday, January 12th, 2012 AT 12:22 AM
Tiny
MAGICBYDZN
  • MEMBER
  • 7 POSTS
I'll look into the codes tomorrow, too dark now :(
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Thursday, January 12th, 2012 AT 2:37 AM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,870 POSTS
Alright keep me posted.
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Thursday, January 12th, 2012 AT 3:03 AM
Tiny
MAGICBYDZN
  • MEMBER
  • 7 POSTS
Ok, I still need to get the codes from computer. But as a test I closed off the IAC port and unplugged the IAC Valve. Car runs fine! When I plug it back in the IAC Valve opens all the way and stays open, letting too much air into the intake. I'm thinking a short in the computer to the IAC Valve is sending power all the time to the IAC Valve, even when the car is off. If I reset the Copmuter could that help? To say the car was in bad shape when I got it would be an understatment.
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Thursday, January 12th, 2012 AT 7:09 PM
Tiny
SATURNTECH9
  • MECHANIC
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What size engine do you have so I can get the correct wire diagram for the iac?
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Friday, January 13th, 2012 AT 1:56 AM
Tiny
SATURNTECH9
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Heres the wire diagram we need to see if there are any codes in the computer.
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Friday, January 13th, 2012 AT 2:02 AM
Tiny
SATURNTECH9
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Here is the trouble tree for the iac.
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Friday, January 13th, 2012 AT 2:10 AM
Tiny
MAGICBYDZN
  • MEMBER
  • 7 POSTS
The Engine is a 1.6
I checked and there is no vacuum leaks. If I close the IAC all the way it will idle and run normal. If I plug in the IAC it will open all the way with the RPMs running up to 2000+ and keep running that high no matter how hot the car gets. The IAC makes a Clicking Sound all the time, even with the car off. But if I reset the computer it will stop, until I try to run the car again. Then clicking comes back and keeps clicking even when the car is off. I'm thinking a bad ECM?
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Friday, January 20th, 2012 AT 6:22 PM
Tiny
SATURNTECH9
  • MECHANIC
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Have you went thru the iac diagnoses I posted to rule out other issues besides the ecm?
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Saturday, January 21st, 2012 AT 12:00 AM

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