High Idle - Still
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From: Florida
High Idle - Still
I had my shop install a new idle control valve on my 1987 S4 automatic because the old one was not responding to input and was idling high all the time. Along with new idle control valve I had the injectors cleaned and balanced, and the throttle body cleaned. Now the car idles correctly when cold but still idle high when hot. I was told the temperature sensors are all working and the idle valve responses to input. What could be causing a hot high idle?
Tommy
Tommy
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From: Saskatoon Sask. Can.
Tommy,
I had the same problem. I have a diagnostic tester made by John Speakes that will also reset the idle parameters in the computer. http://www.jdsporsche.com/jdsdiagtool.html. I am sure there are other tools out there that will work. No more problems in my case. Make sure you dont have any other vacuum leaks before doing this.
I had the same problem. I have a diagnostic tester made by John Speakes that will also reset the idle parameters in the computer. http://www.jdsporsche.com/jdsdiagtool.html. I am sure there are other tools out there that will work. No more problems in my case. Make sure you dont have any other vacuum leaks before doing this.
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From: Florida
Thanks everyone for your help. The shop has tested the MAF and throttle switch and they were okay. Unfortunately diagnostic plug-in only started in MY 1988 so my 1987 cannot benefit from the fault code/resetting tool 
It's beginning to look like it could be the LH.
Tommy
It's beginning to look like it could be the LH.
Tommy
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From: Las Vegas
Just try unhooking the cable from the throttle linkage on the side of the plenum.?
You said you have tested your throttle switch but if your cables arent adjusted correctly maybe the switch isnt being acivated. The srping in the trottle plate assembly is more than strong enough to close the throttle plate and activate the switc....unless the cables wont let it. I was just messing around with this today on Darriens 86.5 , a supercharger iinstall, the smallest adjustment can activate that switch. If it doesnt, your idle is high.
If you disconnect the linkage, try and keep some tension on it, or atleast be careful as with slack on the cable it may slip off the pulley underneath.
Just some ideas.
You said you have tested your throttle switch but if your cables arent adjusted correctly maybe the switch isnt being acivated. The srping in the trottle plate assembly is more than strong enough to close the throttle plate and activate the switc....unless the cables wont let it. I was just messing around with this today on Darriens 86.5 , a supercharger iinstall, the smallest adjustment can activate that switch. If it doesnt, your idle is high.
If you disconnect the linkage, try and keep some tension on it, or atleast be careful as with slack on the cable it may slip off the pulley underneath.
Just some ideas.
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From: Cambridge England
Tommy928
Your 87 car LH and EZK ECUs can be upgraded to diagnostics with a simple change of EPROMs.
You are correct that one early sign of LH failure can be no drive to the ISV, but check everything else out that people have mentioned already.
How many miles on the car ?
Your 87 car LH and EZK ECUs can be upgraded to diagnostics with a simple change of EPROMs.
You are correct that one early sign of LH failure can be no drive to the ISV, but check everything else out that people have mentioned already.
How many miles on the car ?
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Thread Starter
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Joined: Jul 2002
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From: Florida
Thanks for all the suggestions.
John - my car has 104K miles on it but the LH was replaced by the dealer at 70K. If I install the new EPROMs will I be able to perform the idle stablization loop to correct the idle? My shop will test the LH next.
Thanks,
Tommy
John - my car has 104K miles on it but the LH was replaced by the dealer at 70K. If I install the new EPROMs will I be able to perform the idle stablization loop to correct the idle? My shop will test the LH next.
Thanks,
Tommy
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From: SoCal
The idle switch (not TPS) needs to be checked with an ohmmeter (pin 2 of LH)
or a test light, and NOT assumed to be functional because of a clicking sound.
Also, the idle valve signal (pin 33 of the LH) needs to be checked with a LED
test light (flashing) or an o-scope (square wave).
As mentioned, air leaks which bypass the idle valve will cause a high idle.
There's no need to use a diagnostic tool to "fix" an idle problem if the system
is functioning properly.
or a test light, and NOT assumed to be functional because of a clicking sound.
Also, the idle valve signal (pin 33 of the LH) needs to be checked with a LED
test light (flashing) or an o-scope (square wave).
As mentioned, air leaks which bypass the idle valve will cause a high idle.
There's no need to use a diagnostic tool to "fix" an idle problem if the system
is functioning properly.
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From: Cambridge England
Tommy928
I had assumed that when the ISV was changed, then hoses etc which might leak in false air would also be attemded to.
You shouldn't need to run the diagnostic idle adaptation unless the MAF is badly aged. If it is aged too far, then it may never be able to get the idle stabilised.
Perhaps your shop can swap another known good MAF in there.
But, as said before check the other things that have been mentioned.
I had assumed that when the ISV was changed, then hoses etc which might leak in false air would also be attemded to.
You shouldn't need to run the diagnostic idle adaptation unless the MAF is badly aged. If it is aged too far, then it may never be able to get the idle stabilised.
Perhaps your shop can swap another known good MAF in there.
But, as said before check the other things that have been mentioned.