LT4 High constant idle
Thread Starter
Safety Car
Joined: Sep 2006
Posts: 4,129
Likes: 1
From: Pasadena CA
LT4 High constant idle
Hi all
Well I just went through sa bunch of posts and didn't quite find what I'm looking for, but got some good pointers.
Problem - high idle - around 970 to 1000 rpm at normal operating temps. It's a good constant idle and engine otherwise runs great.
Car - 96 LT4, had it for 2 weeks now. Also ECM has been altered with Hypertech reprogrammer which I got with the car but haven't plugged in or tried to use yet.
I also chucked a bottle of injector cleaner into the last full tank - this problem may or may not have started since I did this. Also the previous owner told me he had just cleaned out the t/b and he was a pretty knowledgable guy and looked after the car mechanically.
Additionaly I've noticed in traffic, the throttle sticks very slightly when in 1st at very slow speed, trying to match speed with very slow moving traffic. It's not bad, just a bit annoying and something I want to fix. Would these two things be related?
My Chilterns manual says you can't adjust idle manually and basically says don't mess with it, it needs programming. Would the Hypertech have messed up idle rpm settings? Or is something mechanical sticking that I can fix myself. I found a thread about TV cable adjustment, but I have a 6-speed.
thanks!
-Eaks
Well I just went through sa bunch of posts and didn't quite find what I'm looking for, but got some good pointers.
Problem - high idle - around 970 to 1000 rpm at normal operating temps. It's a good constant idle and engine otherwise runs great.
Car - 96 LT4, had it for 2 weeks now. Also ECM has been altered with Hypertech reprogrammer which I got with the car but haven't plugged in or tried to use yet.
I also chucked a bottle of injector cleaner into the last full tank - this problem may or may not have started since I did this. Also the previous owner told me he had just cleaned out the t/b and he was a pretty knowledgable guy and looked after the car mechanically.
Additionaly I've noticed in traffic, the throttle sticks very slightly when in 1st at very slow speed, trying to match speed with very slow moving traffic. It's not bad, just a bit annoying and something I want to fix. Would these two things be related?
My Chilterns manual says you can't adjust idle manually and basically says don't mess with it, it needs programming. Would the Hypertech have messed up idle rpm settings? Or is something mechanical sticking that I can fix myself. I found a thread about TV cable adjustment, but I have a 6-speed.
thanks!
-Eaks
Melting Slicks
Joined: Dec 1999
Posts: 2,816
Likes: 2
From: Austin, TX
It's possible the problems are related. If the throttle linkage is sticking, that could cause the throttle to not close all the way (high idle) as well as your sticky off-throttle problem. (I had this same thing on mine)
With the car running (parking brake set
), pop the hood and try moving the throttle by hand. Can you make it idle correctly if you push it closed? Don't lay on it or anything -- just small pressure. Similarly, do you feel the same sticking when you try to open the throttle by hand? If that is the problem, clean the inside of the tb (butterflies) with TB cleaner and also the linkage (around the spring and the shaft). That should help.
You should also check to make sure the throttle cable is releasing all the way. If your cruise control or ASR module is out of adjustment, it can cause a high idle as well.
With the car running (parking brake set
), pop the hood and try moving the throttle by hand. Can you make it idle correctly if you push it closed? Don't lay on it or anything -- just small pressure. Similarly, do you feel the same sticking when you try to open the throttle by hand? If that is the problem, clean the inside of the tb (butterflies) with TB cleaner and also the linkage (around the spring and the shaft). That should help.You should also check to make sure the throttle cable is releasing all the way. If your cruise control or ASR module is out of adjustment, it can cause a high idle as well.
Thread Starter
Safety Car
Joined: Sep 2006
Posts: 4,129
Likes: 1
From: Pasadena CA
Well I checked it out - the thottle seems to be returning correctly and there is no further movement possible. The thing that appears to be stopping the throttle lever is a screw-adjustment with an impossible-to-get-to cross-head/ Philips screw inside a metal tunnel. It looks like I could just screw this out a couple of threads with the right tool and maybe the throttle arm will close a bit more..
But the Chiltern manual totally put me off with the whole dont f^&* with it attitude, so I think I'm going to have to take it in somewhere to get the idle speed adjusted.
I guess this is my first experience of the awkward to work on LT I heard so much about
p.s I also set Hypertech programmer back to stock tune and it did nothing to idle speed (and lost noticeable torque too - those things do work!)
-cheers
But the Chiltern manual totally put me off with the whole dont f^&* with it attitude, so I think I'm going to have to take it in somewhere to get the idle speed adjusted.
I guess this is my first experience of the awkward to work on LT I heard so much about
p.s I also set Hypertech programmer back to stock tune and it did nothing to idle speed (and lost noticeable torque too - those things do work!)
-cheers
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by Eakster
Well I checked it out - the thottle seems to be returning correctly and there is no further movement possible. The thing that appears to be stopping the throttle lever is a screw-adjustment with an impossible-to-get-to cross-head/ Philips screw inside a metal tunnel. It looks like I could just screw this out a couple of threads with the right tool and maybe the throttle arm will close a bit more..
But the Chiltern manual totally put me off with the whole dont f^&* with it attitude, so I think I'm going to have to take it in somewhere to get the idle speed adjusted.
I guess this is my first experience of the awkward to work on LT I heard so much about
p.s I also set Hypertech programmer back to stock tune and it did nothing to idle speed (and lost noticeable torque too - those things do work!)
-cheers
But the Chiltern manual totally put me off with the whole dont f^&* with it attitude, so I think I'm going to have to take it in somewhere to get the idle speed adjusted.
I guess this is my first experience of the awkward to work on LT I heard so much about
p.s I also set Hypertech programmer back to stock tune and it did nothing to idle speed (and lost noticeable torque too - those things do work!)
-cheers
Good luck..
