LT1 Low idle when cold
Thread Starter
Safety Car
Joined: Oct 2000
Posts: 4,234
Likes: 355
From: Albuquerque, NM
LT1 Low idle when cold
This used to be an intermittent problem so I didn't worry about it, but now it does it all the time. When I first start my '92 LT1 six speed, the idle is very low (200 RPM) unless I open the throttle. Sometimes the engine will die. However, after driving the car for a bit it the idle seems to be almost normal, although it may still be just a little low.
I had the throttle body apart and cleaned out the IAC pintle and bore about a year (5,000 miles) ago, so I don't think it's dirty. Also the fact that it started as an intermittent problem suggests some electical problem.
I plan to replace the IAC motor, but I just wanted to see if anyone has any other suggestions first. Thanks!!
I had the throttle body apart and cleaned out the IAC pintle and bore about a year (5,000 miles) ago, so I don't think it's dirty. Also the fact that it started as an intermittent problem suggests some electical problem.
I plan to replace the IAC motor, but I just wanted to see if anyone has any other suggestions first. Thanks!!
Thread Starter
Safety Car
Joined: Oct 2000
Posts: 4,234
Likes: 355
From: Albuquerque, NM
When I took it apart I was careful not to change the adjustment, but I did not check it. I thought that was something that was adjusted automatically by the ECM.
I'll probably replace the IAC, but I'll check that distance when I take it apart. Anyway, it started and idled just fine this morning, so it's definitely an intermittent problem.
THANKS for the help!!
I'll probably replace the IAC, but I'll check that distance when I take it apart. Anyway, it started and idled just fine this morning, so it's definitely an intermittent problem.
THANKS for the help!!
Drifting
Joined: Jun 2002
Posts: 1,945
Likes: 41
From: Corinth TX
I know this may be reaching but I recently had the same problem. I fixed the problem by mistake actually since I was trying to get the car to pass emissions for my State Inspection. I changed the sparkplugs andlow and behold the car runs like a new car. No more idle problems and it runs great!! I know some like to run the AC Delco plugs but I put in some NGK-TR55s and damn this car seems totally different. The TR-55s are the copper plugs in contrast to the Iridium versions. I have heard that the copper ones produce a better spark. I had a spare set for my C5 and put them in the C4 and like I said, the car runs great!! This may be an option to check. Goodluck in your search.
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Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Originally Posted by SunCr
PS: Make sure the a/c is off - if the fan(s) are running - the ECM thinks it's at least 217 (if I remember the threshold for the '92 correctly). Troubleshoot the CTS accordingly.
Thread Starter
Safety Car
Joined: Oct 2000
Posts: 4,234
Likes: 355
From: Albuquerque, NM
I have an EASE computer based diagnostic tool that I bought on the forum a while back that I've never used. I'll have to try to get it going and check the CTS.
I know there are actually two coolant temp sensors, one for the digital gage and one for the analog. Which one does the ECM use? I assume the one for the digital display.
If that CTS is faulty, wouldn't I be getting a faulty reading on the digital temperature readout?
Thanks again!
I know there are actually two coolant temp sensors, one for the digital gage and one for the analog. Which one does the ECM use? I assume the one for the digital display.
If that CTS is faulty, wouldn't I be getting a faulty reading on the digital temperature readout?
Thanks again!
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Originally Posted by BlackbirdZ07
I have an EASE computer based diagnostic tool that I bought on the forum a while back that I've never used. I'll have to try to get it going and check the CTS.
I know there are actually two coolant temp sensors, one for the digital gage and one for the analog. Which one does the ECM use? I assume the one for the digital display.
If that CTS is faulty, wouldn't I be getting a faulty reading on the digital temperature readout?
Thanks again!
I know there are actually two coolant temp sensors, one for the digital gage and one for the analog. Which one does the ECM use? I assume the one for the digital display.
If that CTS is faulty, wouldn't I be getting a faulty reading on the digital temperature readout?
Thanks again!
Race Director
Joined: Aug 2003
Posts: 13,421
Likes: 8
From: Lake Mary Florida
When you started up the engine after R&R'ing the throttle body and IAC, did you set the idle electronically. That is on the first start, press and hold the accelerator pedal and start the engine. Let it run for 2 seconds then off. Restart and let it idle.
Race Director
Joined: May 2001
Posts: 14,165
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FWIW once the IAC has been run on the car they specifically tell you NOT to mess with it by hand because you can break it. I'm not sure if it's some kind of worm gear that just isn't engaged until first year or what.
Thread Starter
Safety Car
Joined: Oct 2000
Posts: 4,234
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From: Albuquerque, NM
Originally Posted by Jet-Jock
When you started up the engine after R&R'ing the throttle body and IAC, did you set the idle electronically. That is on the first start, press and hold the accelerator pedal and start the engine. Let it run for 2 seconds then off. Restart and let it idle.
Thread Starter
Safety Car
Joined: Oct 2000
Posts: 4,234
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From: Albuquerque, NM
Originally Posted by Nathan Plemons
FWIW once the IAC has been run on the car they specifically tell you NOT to mess with it by hand because you can break it. I'm not sure if it's some kind of worm gear that just isn't engaged until first year or what.
Race Director
Joined: Aug 2003
Posts: 13,421
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From: Lake Mary Florida
TPS requires connecting a Tech 1 and running the learn idle program. I mis-stated earlier it's learn throttle position on the IAC start sequence. Procedure is still applicable, but after this much time I can't say whether it will do any good. I believe it performs a step count to set the IAC.
Generally just spraying the pintel end with throttle body cleaner is good enough.
Adjustments are only recommended for new IAC's, prior to installing you take a specific measurement and if it's greater you gently press.
Generally just spraying the pintel end with throttle body cleaner is good enough.
Adjustments are only recommended for new IAC's, prior to installing you take a specific measurement and if it's greater you gently press.
Last edited by Jet-Jock; Jan 17, 2006 at 08:18 PM.
Melting Slicks
Joined: Oct 2004
Posts: 2,283
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From: Leeds Alabama
I believe that on the LT1 there are TWO coolant temp sensors, the one on the water pump is for your gauges and the one on the engine is for your ecm. If you check the readout on the CCM you get the same data the ecm is reading.
Safety Car
Joined: Feb 2002
Posts: 4,212
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From: Sun City West Az
Originally Posted by corvette1989bham
I believe that on the LT1 there are TWO coolant temp sensors, the one on the water pump is for your gauges and the one on the engine is for your ecm. If you check the readout on the CCM you get the same data the ecm is reading.
