[Diy_efi] Out of the blue high idle

[Joe Lutz]

Going by what you said, the ecm is opening the IAC valve causing it to idle 
high.  This leads me to believe there is not a problem with the IAC, but 
something causing the ecm to want to make the engine idle high such as a bad 
or incorrectly adjusted TPS.  I don't think the TPS position is adjustable 
on those throttle bodies though.  Did you try to unplug the TPS?  You may 
also want to remove the TPS from the Throttle body, but leave the connector 
attached so the sensor can travel all the way back.  I had this exact same 
problem with a TBI 454 not long ago and I could just push on the little 
lever that goes to the TPS sensor toward the closed position and it would 
idle down.  New TPS fixed it.
If you are so inclined, you may want to put a volt meter on the middle wire 
of the TPS with the other lead grounded with the switch on and engine off.  
Work the throttle to see if the voltage changes with throttle position.  
Also look for any weird spikes around closed throttle that would indicate a 
bad spot on the TPS.  All the TPS is is a potentiometer.  Do you by any 
chance have access to a scan tool or know how to datalog?

Joe



From: "Jim Yeagley" <jyeag at core.com>
>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
>Subject: Re: [Diy_efi] Out of the blue high idle
>Date: Fri, 4 Jul 2003 08:19:39 -0400
>
>Here's something I vaguely remember, when changing the position of the IAC,
>the ECM needs to find the closed position for the valve to assign that
>position to zero.  This was done by driving the vehicle over 35 mph for 
>some
>short amount of time.
>
>Jim Yeagley
>
>----- Original Message -----
From: "TomQ" <zippy at tomquinn.com>
>
> > Thanks for the advice Joe! I tried the "plug small port in the top of 
>the
> > throttle
> > body that feeds the IAC valve passage". That is it. The idle came way 
>down
> > right away. I cleaned the snot out of the passage way but it still is
>open.
> > I then pulled the valve out a little so it plugs the hole. It did and 
>the
> > idle was down around 600. I then kept revving the motor up and down and
>the
> > idle slowly crept up. I stopped at 1200 rpm. I am going to take a look 
>at
>my
> > program to make sure the idle is correctly stated. Any way can take some
> > volt measurements to see if the valve is being "told" to open more then 
>it
> > should?
> >
> > -TomQ
>
>
>
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