Will measuring the idle adjustment screw work?
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Lead Driver
Joined: Oct 2016
Posts: 6,185
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From: Houston/Sugar Land
Will measuring the idle adjustment screw work?
I was wondering if physically measuring the Idle Adjustment Screw with a caliper would work to restore my original setting.
I have compromised my IAS and have access to a non-compromised screw. When the two screws are measured from the top of the screw to the T body the measurement of the open distance of the throttle stop areas are different. I could bend my stop to conform to the non-compromised one but I am asking for advise first.
As I understand, the voltage determines the adjustment and the question is can it be done by measurement. Thank You
I have compromised my IAS and have access to a non-compromised screw. When the two screws are measured from the top of the screw to the T body the measurement of the open distance of the throttle stop areas are different. I could bend my stop to conform to the non-compromised one but I am asking for advise first.
As I understand, the voltage determines the adjustment and the question is can it be done by measurement. Thank You
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
The simple way is to adjust it until the throttle blades are just barely cracked open from fully closed. The sole purpose it provides is preventing the throttle blades from closing too far then sticking in the bore.
When adjusted this way the idle RPM should be very low or the engine may die with the IAC disconnected. This is perfectly normal. In this state the TPS output should be between 0.6 to 1.0 VDC. If not, replace the TPS.
If the idle RPM remains high, IAC disconnected, you have a vacuum leak or worn out throttle body.
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Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
After taking off and cleaning the butterfly valves I noticed they would stick when it was shut all the way like you said. I adjusted the screw just to the point of no resistance to open them and barely being free when I let them close with force first. With that screw in all the way those butterflies will not open. Before I re-installed the TB, I thought about the measuring aspect as a possible solution.
You know I have been fighting this 1K+ RPM rough idle since day one. Based on your opinion of a vac leak I retested again with a smoke machine. Third time, no smoke leaks and no change. I borrowed the other TB with the non compromised screw that I was using to measure and put it on the truck. NO CHANGE. For review I have replaced the EGR, PCM,MAP,ICM, Faulty smog pump,PCV, TPS, spark plugs, new wires, new distributor and new coil, new fuel injectors,IAC and that borrowed TB. Can I live with it? Yes. Do I want to? NO. I am in total agreement with the vac leak you suggest being the culprit but I can't find it IF that is the cause.
I just started it and pulled the IAC plug with the borrowed TB and no change in idle.
You know I have been fighting this 1K+ RPM rough idle since day one. Based on your opinion of a vac leak I retested again with a smoke machine. Third time, no smoke leaks and no change. I borrowed the other TB with the non compromised screw that I was using to measure and put it on the truck. NO CHANGE. For review I have replaced the EGR, PCM,MAP,ICM, Faulty smog pump,PCV, TPS, spark plugs, new wires, new distributor and new coil, new fuel injectors,IAC and that borrowed TB. Can I live with it? Yes. Do I want to? NO. I am in total agreement with the vac leak you suggest being the culprit but I can't find it IF that is the cause.
I just started it and pulled the IAC plug with the borrowed TB and no change in idle.
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
One way to check your vacuum lines, is to disconnect all vacuum lines at the intake and cap off the connections. They are all usually close or on the same tree, sometimes there is another vacuum port under the TB.
The exceptions are the MAP and Fuel Regulator, if you have them (Necessary for Fuel/Air Mixture), what I do is buy a new piece of hose, and temporarily hook these devices up to the ports where you remove the existing hoses. I like to hook in a vacuum gauge as well.
Or you can try them one at a time....
This eliminates all the existing hoses, if it makes a difference, start re-connecting the hoses one at a time until you find the culprit.
This does not address the Intake/TB potential Gasket leaks.
The exceptions are the MAP and Fuel Regulator, if you have them (Necessary for Fuel/Air Mixture), what I do is buy a new piece of hose, and temporarily hook these devices up to the ports where you remove the existing hoses. I like to hook in a vacuum gauge as well.
Or you can try them one at a time....
This eliminates all the existing hoses, if it makes a difference, start re-connecting the hoses one at a time until you find the culprit.
This does not address the Intake/TB potential Gasket leaks.
Last edited by vjsimone; Feb 17, 2017 at 10:50 PM. Reason: Adding text
Thread Starter
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Lead Driver
Joined: Oct 2016
Posts: 6,185
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From: Houston/Sugar Land
[QUOTE=vjsimone;16960391]One way to check your vacuum lines, is to disconnect all vacuum lines at the intake and cap off the connections. They are all usually close or on the same tree, sometimes there is another vacuum port under the TB.
The exceptions are the MAP and Fuel Regulator, if you have them (Necessary for Fuel/Air Mixture), what I do is buy a new piece of hose, and temporarily hook these devices up to the ports where you remove the existing hoses. I like to hook in a vacuum gauge as well.
This eliminates all the existing hoses, if it makes a difference, start replacing the hoses one at a time until you find the culprit.
That sounds like a simple way to check them for a novice like me, but I used and watched a professional smoke machine and easily found one leak early on. I'll try just about anything now except running out of money and having to go back to work. Look at my last post. I am revising my resume now just in case.
Anyway gotta go change the air in my tires. Thank you. Sandy
The exceptions are the MAP and Fuel Regulator, if you have them (Necessary for Fuel/Air Mixture), what I do is buy a new piece of hose, and temporarily hook these devices up to the ports where you remove the existing hoses. I like to hook in a vacuum gauge as well.
This eliminates all the existing hoses, if it makes a difference, start replacing the hoses one at a time until you find the culprit.
That sounds like a simple way to check them for a novice like me, but I used and watched a professional smoke machine and easily found one leak early on. I'll try just about anything now except running out of money and having to go back to work. Look at my last post. I am revising my resume now just in case.
Anyway gotta go change the air in my tires. Thank you. Sandy
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Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
Thanks for the suggestion. I just disconnected the hose after starting and plugged the hose with my hand and it maintained the idle it had when connected. When I removed my hand the idle would rise and continued to until I plugged it. If there is something I missed please let me know and I am happy to try it. Thanks Sandy
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Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
One way to check your vacuum lines, is to disconnect all vacuum lines at the intake and cap off the connections. They are all usually close or on the same tree, sometimes there is another vacuum port under the TB.
The exceptions are the MAP and Fuel Regulator, if you have them (Necessary for Fuel/Air Mixture), what I do is buy a new piece of hose, and temporarily hook these devices up to the ports where you remove the existing hoses. I like to hook in a vacuum gauge as well.
The exceptions are the MAP and Fuel Regulator, if you have them (Necessary for Fuel/Air Mixture), what I do is buy a new piece of hose, and temporarily hook these devices up to the ports where you remove the existing hoses. I like to hook in a vacuum gauge as well.
I already sent him down this path on the first few threads for his high idle problem. It is the simplest way to eliminate the various hoses and reservoirs. Based on the smoke test results it appears there are no other leaks, but obviously the engine is getting unmetered air somewhere.
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