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What sensors tell the computer to high idle when its cold. Mine hasn't high idled all winter, no matter how cold it is.
 

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Oil temp and outside air temp. The pcm reads these and signals the ebpv to close.
 

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Auto tranny has to be in park and manual tranny has to have parking brake set (light on) for the cold idle-up to work.
 

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I noticed that even when I have the parking brake engaged the light on the dash doesn't come on. So I guess I'll start checking there.
 

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I noticed that even when I have the parking brake engaged the light on the dash doesn't come on. So I guess I'll start checking there.
Mine has no high idle light? Like said above it must be in park, or parking brake on for standard. Mine starts, then in exactly 2min. the Idle picks up and the exhaust valve closes. You can really hear the difference, sounds like a jet engine warming up. If I touch anything driving related in the truck, like the brake pedal, the rpm drops immediately and the valve opens. This is because the computer thinks your going to drive, and shuts the system down. So try just starting it, don't touch nothing, get out and wait for 5 minutes to see what happens. Are you plugging in at night. Mine doesn't come on when I plug in as its too warm to start the system. I do live in Canada and its cold hear, so I assume if your plugging in then it won't go. If all fails, then I might check the temp. sensors. Most likely oil temp. Is your temp gauge working?
 

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No parking brake light, check the switch on the parking brake, or maybe the dash light is burned out. The plunger on the switch can sometimes stick. I am not aware of a high idle light.
 

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There is no high idle light, he was talking about the parking brake/e-brake light. Mine no longer comes on, but I have an auto tranny so if I'm in park it will still high idle.

For the light, check the switch down by the e-brake peddle, it normally just needs adjustment.
 

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What sensors tell the computer to high idle when its cold.
Primarily the engine oil temp (EOT) sensor. If EOT is less than about 122° F. and the intake air temp (IAT) says it's cold out, then the engine idle RPM will elevate after a coupla minutes if idling. How much the RPM elevates depends on how cold it is. Max is 900 for '99s and 1,300 RPM for 2000-up models when it's really cold.

Mine hasn't high idled all winter, no matter how cold it is.
If all the conditions are met (automagic tranny in park or E-brake mashed if 6-speed handshaker), fat feet not touching anything) that could be either the EOT or IAT sensors, but you should also have an idiot light if one of those sensors is on the blink.

Per the book for my '99 7.3L:

Engine Oil Temperature Sensor
The Engine Oil Temperature sensor is a thermistor mounted to the oil reservoir whose resistance decreases as engine oil temperature increases. The Engine Oil Temperature signal is used by the PCM to calculate fuel quantity, injection timing, glow plug operation and exhaust back-pressure.

At oil temperatures below 50°C (122° F), low idle is increased to a maximum of 900 rpm to increase engine warm-up.
{note: that's for '99 7.3L. For 2000-'03 7.3L, that same book says: "At low ambient air temperatures, and oil temperature below 50°C (122°F), low idle is increased to a maximum of 1300 rpm to increase engine warm-up." There is no '99.5 book, but I suspect the '99.5s use 1,300 as the max elevated idle RPM}
Fuel quantity and timing is controlled throughout the total operating range to provide adequate torque and power.

An Engine Oil Temperature signal detected out of range, high or low, by the PCM will cause the PCM to assume an engine oil temperature of 20° C (68°F) for starting purposes and 100° C (212°F) for operating purposes. The Malfunction Indicator Lamp in the instrument cluster will be illuminated as long as the fault condition exists.

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The Intake Air Temperature (IAT) Sensors
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.

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Fault codes:

code.footnote.circuit.condition............................... probable causes
P0112 b IAT Intake air temp. sensor circuit low input Grounded circuit, biased sensor, PCM
P0113 b IAT Intake air temp. sensor circuit high input Open circuit, biased sensor, PCM, short to 5v
P0197 a, b EOT Engine oil temp. sensor circuit low input Grounded circuit, biased sensor, PCM
P0198 a, b EOT Engine oil temp. sensor circuit high input Open circuit, biased sensor, PCM, short to 5v

The a and/or b footnotes means the MIL (idiot light) will come on.
 

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Discussion Starter #9
I'm leaning toward the switch at the e-brake because I don't have any other indicator lights coming saying something is bad. But I got other issues now, I have a big green puddle under the passanger side of the radiator!
 

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To clarify what Smokey said, the a footnote says:

"(a)Check Engine light illuminates when fault is detected in second drive cycle (California, OBDII calibration)."

I know that the SES did not come on when I forgot to plug the IAT sensor in when I was doing some work once.

If it isn't a sticky parking brake switch, then you should probably get the codes pulled.

Sorry about the green puddle.
 

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I'm also having problems with my High idle engaging. I have a 2002 excursion and one day it just stopped coming on. I have no idiot lights in the dash so I don't know whats up. Maybe it just hasn't gotten cold enough. Any thoughts would help out alot. Thanks
 

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I've had to clean the contacts on the switch on my e-brake pedal a couple of times. It's ready to have it done again. That switch grounds a circuit telling the PCM it can start the high idle.

I know in my dad's '03 6.0L auto I can't figure out what I need to do to get it to idle up. seems it'll just do it when it feels like it.
 
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