idle adjustment
Thread Starter
Le Mans Master
Joined: Jul 2004
Posts: 6,228
Likes: 698
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
idle adjustment
Took off my throttle body the other day with the intention of doing a thorough cleaning. The screws on the top plate came right off, but the other ones were a problem. I snapped one of, so I said won't do that again and stopped. I just cleaned the throttle plate and port really good and put it back together. Idle was much faster before. I didn't touch the IPS. Would just cleaning the little I did make that much difference? I reset the idle and adjusted the IPS to the recommended .52 volts. It still idles at almost 700 RPM's. What did I miss? Thanks.
Last edited by Cruisinfanatic; Jul 11, 2005 at 01:20 PM.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
It's likely that a thin layer of gunk that you removed is letting in more air at idle, though 700rpm is not a bad idle.
If you want to reset idle, remove the IAC from under the TB and clean it's pintle & bore. Then reset base idle to 450rpm, per instructions on my site. Finally, with the idle still set to 450rpm, adjust the TPS base & WOT settings.
If you want to reset idle, remove the IAC from under the TB and clean it's pintle & bore. Then reset base idle to 450rpm, per instructions on my site. Finally, with the idle still set to 450rpm, adjust the TPS base & WOT settings.
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
I had a similar situation.
After I bought my 86' last year I cleaned the throttle body.
WHen I put it back on the idle went from 900 in neutral/7-800 in gear to 1300 in neutral/1000 in gear. It made the car difficult to drive. The idle adjustment screw cover was still on, so apparently it had never been touched. I went through the IAC/TPS check procedure, but it didn't fix/help the problem. Finally I popped the cover off and set the base idle and that helped a lot. It now idles 6-700 in gear and 700 in neutral. It is not perfect, but it needs new injectors, so I won't ask too much of it.
After I bought my 86' last year I cleaned the throttle body.
WHen I put it back on the idle went from 900 in neutral/7-800 in gear to 1300 in neutral/1000 in gear. It made the car difficult to drive. The idle adjustment screw cover was still on, so apparently it had never been touched. I went through the IAC/TPS check procedure, but it didn't fix/help the problem. Finally I popped the cover off and set the base idle and that helped a lot. It now idles 6-700 in gear and 700 in neutral. It is not perfect, but it needs new injectors, so I won't ask too much of it.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by Joslinm
I reset the idle and adjusted the IPS...
If all that is set correctly, chances are you have a vacuum leak left from the recent work.
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Burning Brakes
Joined: Nov 2004
Posts: 834
Likes: 1
From: Keller Texas
I have had some problems with the idle as well. I have a LT4 that has been rebuilt and the air injection has been removed. I have not had the $ to have it tuned yet but what can I do to help the idel? What web site are you refering to that will help?
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by RED LT4
What web site are you refering to that will help?
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Burning Brakes
Joined: Nov 2004
Posts: 834
Likes: 1
From: Keller Texas
Originally Posted by CFI-EFI
The one I named in my post. I'm not sure how much of this applies to Gen II engines and OBD II. Removing the air injection shouldn't affect the idle. If it was just a rebuild, you must have a vacuum leak, too.
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RACE ON!!!
Doesnt the vacume lines start at the intake and go from there? Cruise controll works fine if that matters at all.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
All vacuum lines have the intake manifold as the eventual source of their vacuum. A vacuum leak doesn't necessarily render ALL vacuum operated devices inoperative. Also, vacuum lines are not the only possible sources of a vacuum leaks.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
OB 2 motors have a slew of codes for TPS failures and 3 or so for the IAC circuit. If you have a Check Engine Light, suspect one of these codes and then follow the Trouble Tree Chart for the Code.
For any year, a scanner simplifies the diagnostics. Check targeted RPM and IAC counts. If 0 counts and the idle is high (which is considered to be 50 rpms greater than what the ECM is targeting while in Drive or 100 rpms in Park or Neutral), extra air is coming in from another source, but anytime you have 0 counts, it isn't working as it should. If the counts are remarkably high (most injected motors show 12 to 25 with the a/c off - add 10 to 20 more with the a/c on), the ECM isn't controlling the IAC (or if it's stuck somewhere in the 100's, it thinks you're about to start it).
If you've replaced the IAC or removed it for cleaning or disconnected while it's running, press the accelerator slighty and start it - let it run for 10 seconds, then off for 5. Restart and check idle.
For any year, a scanner simplifies the diagnostics. Check targeted RPM and IAC counts. If 0 counts and the idle is high (which is considered to be 50 rpms greater than what the ECM is targeting while in Drive or 100 rpms in Park or Neutral), extra air is coming in from another source, but anytime you have 0 counts, it isn't working as it should. If the counts are remarkably high (most injected motors show 12 to 25 with the a/c off - add 10 to 20 more with the a/c on), the ECM isn't controlling the IAC (or if it's stuck somewhere in the 100's, it thinks you're about to start it).
If you've replaced the IAC or removed it for cleaning or disconnected while it's running, press the accelerator slighty and start it - let it run for 10 seconds, then off for 5. Restart and check idle.
Last edited by SunCr; Jul 11, 2005 at 05:50 PM.
Instructor
Joined: Apr 2004
Posts: 193
Likes: 0
From: peculiar mo
i have been having idle problems with my l98 sometimes its low like 4-500 sometimes goes away after i get moving. sometimes it is high like 1000-1200 barely moving. most of the time it is fine at 7-800. i never know when it is going to do it tough.
