High idle won't work
Veteran/Sheepdog
Joined: Feb 2012
Posts: 6,047
Likes: 110
From: Western AR
I have a deleted pedestal, no butterfly valve (high flow outlet) and mine still goes into high idle when it is cold outside.
Yes, the exhaust valve is involved in the high idle operation. It closes via the arm coming off the pedestal and helps to warm up the engine quicker.
Yes, the exhaust valve is involved in the high idle operation. It closes via the arm coming off the pedestal and helps to warm up the engine quicker.
Butt-Head
Joined: Apr 2004
Posts: 9,448
Likes: 2,934
From: Reed Point, MT
Then you have the only one in existence or someone spent some time rewiring so it could use a newer PCM.
The base idle speed is higher when the engine is cold but there is no programming in an old PCM that will, over a set amount of time, automatically raise the idle speed when it's cold.
Butt-Head
Joined: Apr 2004
Posts: 9,448
Likes: 2,934
From: Reed Point, MT
Information that would have been pertinent in the first post.
Some piece of the enabling criteria is not being seen by the PCM at this point then.
Don't forget that the feature also shuts off if the brake pedal or accelerator pedal is depressed. Obviously the vehicle will not do anything but idle if the idle validation switch is open so that rules out the APP sensor as a problem.
The high idle (in an automatic) cares about oil temperature, the transmission being in park (or at least the PCM seeing a feedback from the park/neutral switch on the transmission "saying" that the transmission is in park), and how long the engine has been idling. That is all (but what do I know, I only have tuned automatic high idle calibrations for four or five years). The backpressure valve portion cares about a little bit more than that, but its function is first dependent on the idle speed.
Elder User
Joined: Jul 2015
Posts: 914
Likes: 4
Nope. Parking brake must be set, on both AT and MT. Not just set, but the light on the dash must be on, because the pcm needs to see the switch on the parking brake pedal saying the brake is on. My switch drove me crazy for a long time, only working intermittently, until I replaced it. No BRAKE light on, no high idle
There's your problem. Depressing the clutch ( or the "regular" brake pedal)
cancels high idle. Bypassing your NSS means the pcm thinks your clutch pedal is ALWAYS pushed in, so high idle will never set.
Along with the high idle not working, given the amount of torque these things make, even at idle, bypassing the NSS is probably not a great idea. If the truck starts in gear, it can "drive through" the parking brake and hit something.
I found this on TDS:
Diesel Forum - TheDieselStop.com - View Single Post - Have a question about the stock high idle
There's your problem. Depressing the clutch ( or the "regular" brake pedal)
cancels high idle. Bypassing your NSS means the pcm thinks your clutch pedal is ALWAYS pushed in, so high idle will never set.
Along with the high idle not working, given the amount of torque these things make, even at idle, bypassing the NSS is probably not a great idea. If the truck starts in gear, it can "drive through" the parking brake and hit something.
I found this on TDS:
Diesel Forum - TheDieselStop.com - View Single Post - Have a question about the stock high idle
The idle up and the exhaust back pressure controls are both part of the cold ambient pkg (CAP), which is a subroutine in the computer program (PCM) that controls your engine.
Engine Oil Temperature (EOT) Sensor:
At oil temperatures below 50°C (122° F), low idle is increased to a maximum of 900 rpm to increase engine warm-up. (Normal idle RPM is 650 for hand shaker trannies, or 670 for automagics.)
Intake Air Temperature (IAT) Sensor
The IAT signal provides air temperature information to the PCM. The PCM uses the air temperature information to operate the Exhaust Back Pressure (EBP) system and to determine the cold idle setpoint. During long idle periods at cold ambient temperatures, the setpoint will increase engine rpm.
Exhaust Back-Pressure Sensor
The exhaust back-pressure is controlled by the PCM to provide more heat to the coolant for cab heating when ambient air temperature is below 7° C (45°F) and engine oil temperature is below 75°C (167°F) during low load, low speed operating conditions.
In addition to the right temps, the parking brake must be set and a manual tranny in neutral (without a foot on the clutch or go pedal) before high idle will occur.
But the EBPV will close or partially close regardless of tranny and clutch position. That "vacuum cleaner" sound is a result of the EBPV being closed or partially closed, even when driving a cold truck down the road.
For a '99 with a stock tune, high idle is only 900 RPM. But if you have a PCM code (tune or computer program) from a later model 7.3L (or a custom tune), the high idle might be as high as 1,300 RPM in really cold conditions. (And some custom tunes delete the CAP altogether).
Neither the high idle nor the closed EBPV will happen immediately after all conditions are right. The PCM waits a minute or so after conditions are right before it elevates the idle RPM or closes the EBPV.
How much the idle RPM increases, and how much the EBPV closes, depends on how cold are the temps reported by the EOT and IAT sensors. Max closing of the EBPV and max idle RPM requires temps colder than a well digger's hiney.
Diagnosis of CAP problems requires checking several electronic components/switches, after you are sure your custom tune (if any) includes the CAP subroutines.
IAT sensor
EOT sensor
EBP sensor
Parking brake sensor
Neutral validation switch (manual tranny)
Idle validation switch
Engine Oil Temperature (EOT) Sensor:
At oil temperatures below 50°C (122° F), low idle is increased to a maximum of 900 rpm to increase engine warm-up. (Normal idle RPM is 650 for hand shaker trannies, or 670 for automagics.)
Intake Air Temperature (IAT) Sensor
The IAT signal provides air temperature information to the PCM. The PCM uses the air temperature information to operate the Exhaust Back Pressure (EBP) system and to determine the cold idle setpoint. During long idle periods at cold ambient temperatures, the setpoint will increase engine rpm.
Exhaust Back-Pressure Sensor
The exhaust back-pressure is controlled by the PCM to provide more heat to the coolant for cab heating when ambient air temperature is below 7° C (45°F) and engine oil temperature is below 75°C (167°F) during low load, low speed operating conditions.
In addition to the right temps, the parking brake must be set and a manual tranny in neutral (without a foot on the clutch or go pedal) before high idle will occur.
But the EBPV will close or partially close regardless of tranny and clutch position. That "vacuum cleaner" sound is a result of the EBPV being closed or partially closed, even when driving a cold truck down the road.
For a '99 with a stock tune, high idle is only 900 RPM. But if you have a PCM code (tune or computer program) from a later model 7.3L (or a custom tune), the high idle might be as high as 1,300 RPM in really cold conditions. (And some custom tunes delete the CAP altogether).
Neither the high idle nor the closed EBPV will happen immediately after all conditions are right. The PCM waits a minute or so after conditions are right before it elevates the idle RPM or closes the EBPV.
How much the idle RPM increases, and how much the EBPV closes, depends on how cold are the temps reported by the EOT and IAT sensors. Max closing of the EBPV and max idle RPM requires temps colder than a well digger's hiney.
Diagnosis of CAP problems requires checking several electronic components/switches, after you are sure your custom tune (if any) includes the CAP subroutines.
IAT sensor
EOT sensor
EBP sensor
Parking brake sensor
Neutral validation switch (manual tranny)
Idle validation switch
Hotshot
Joined: Mar 2014
Posts: 10,750
Likes: 1,065
From: Douglassville, PA
Elder User
Joined: Jul 2015
Posts: 914
Likes: 4
Are you 100% on this one? If you are then mine has been modified somewhere, somehow. Maybe in the live tuning, maybe when the alarm/remote start got installed. My switch worked intermittently for a short time when I bought mine three years ago then stopped altogether and I never addressed it. I also have removed my EBPV when I installed my van turbo and my high idle still lights up when it's supposed to. I kept the pedestal and the solenoid though, hoping to not affect the high idle or set a code (set code's no big deal).
But, as has been posted by others, not all trucks had the programming. Also, since yours is tuned, the cold idle behaviors could have been modified. I would ask your tuner what they did, as far as high idle criteria.
As for the EBPV, etc... It doesn't matters. The EBPV valve operation is an output/action based on other sensor/switch input. I deleted mine completely, with a blank pedestal, and I just left the plug for the solenoid dangling down in the valley. I have the p0475 code, and my high idle still works fine, nearly every morning lately.
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Fleet Mechanic
Joined: Aug 2006
Posts: 1,465
Likes: 17
From: Jacksonville, FL
My 2002 auto idles up to 1200 without the parking brake applied. I was under the impression it was just a MT thing, which would make sense to me......
You may want to avoid talking in absolute terms if you are not 200% sure on the answer, people have a tendency to pick you apart for that lol
You may want to avoid talking in absolute terms if you are not 200% sure on the answer, people have a tendency to pick you apart for that lol
Thread Starter
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New User
Joined: Apr 2016
Posts: 12
Likes: 0
I have tried my truck with and without the parking brake set. The light on the dash does come on when I set it. What's next for me to check? Like I said the intake air sensor made a friends truck idle up when I swapped them temporarily. And I have a new oil temp switch and a clear egr tube and sensor.
Butt-Head
Joined: Apr 2004
Posts: 9,448
Likes: 2,934
From: Reed Point, MT
If the PCM sees that the intake air temperature is not that cold it will not command a raised idle speed.
Elder User
Joined: Sep 2011
Posts: 979
Likes: 4
From: Vancouver
My 99 idles up without the brake being set, so I think that at least some of the trucks just need low oil temp, and an operational exhaust pressure sensor. Cleaning the sensor did not fix mine when I had a problem, though. I replaced the exhaust sensor.
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