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1999 Ford Explorer 4.0 ohv standard 2wd. Idles at 2200-2500

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1999 Ford Explorer 4.0 ohv...
1999 Ford Explorer 4.0 ohv standard 2wd. Idles at 2200-2500 when cold, when it warms up after 45 minutes to an hour, idle surges(###) ###-####to stall. Push the gas pedal and the idle jumps to 2500 and stays there.
Submitted: 2 years ago.Category: Ford
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Answered in 8 hours by:
9/22/2015
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago
sprinkles08
sprinkles08, ASE Certified Technician
Category: Ford
Satisfied Customers: 23,259
Experience: ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
Verified

Hllo and welcome to JustAnswer!

The most likely causes for an issue like you're having are an erratic throttle position signal or vacuum leak, or the IAC not working correctly.

If the TPS has been replaced and the symptoms didn't change then odds are the sensor itself is ok but there could be a TPS wiring issue altering the signal.

I'm assuming that you've checked or vacuum leaks using carb cleaner.

The problem may be with the IAC driver circuit. If the circuit wiring is open or shorted or the IAC driver in the engine controller fails then it will prevent the IAC from moving and therefore idle can't be properly controlled. The first step in diagnosing the problem is checking for fault codes. Do you know if any codes are setting?

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Customer reply replied 2 years ago
No codes are present or pending. After 45-60 minutes of driving the car behaves properly. No vacuum leaks.
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

Are you able to monitor data or actuate the IAC?

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Customer reply replied 2 years ago
I can monitor live data. Long term and short term vary from -18 to +7, and that range closes when it finally runs correctly. I do not know how to actuate the IAC.
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

What is the TPS voltage when it's idling high?

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Customer reply replied 2 years ago
Sorry for the delay, work has been a challenge and hit the sack at 10:00 Eastern time.I checked volatages on all three wires on the TPS, left to right, at high idle:
5.3 (signal voltage, I assume)
0.95
0.11When I disconnect the TPS, it actually runs better.I have two pending codes: 0172 & 0175.
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

Using the scan tool to monitor the voltage with sensor plugged in what do you see?

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Customer reply replied 2 years ago
My scan tool does % only. Key on, engine not running, 16.1% at 'idle'. At WOT - 75.6%Engine running, 2400 rpm idle - 18.3%
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

It should be zero percent with the throttle closed. Is anything physically holding the throttle blade slightly open?

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Customer reply replied 2 years ago
Not at all. I've switched out throttle body and TPS - STILL there. Now, it's 17.6% not running, start it up, zooms to 3000 rpm, drops to 2200, then drops to 800. TP reading remains at 17% throughout. New TPS ( the third new one). Can it be 'reset' to 0%
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

It should learn on it's own within a few minutes. Does the scan tool have a function worded similarly to 'relearn minimum TPS'?

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Customer reply replied 2 years ago
No, it does not.
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

With the sensor plugged in can you backprobe on the signal wire and see what the voltage is? The scan tool percent may not be reliable.

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Customer reply replied 2 years ago
Do I check the voltage between A and B or A and Ground?
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

Ground the black meter lead and use the red lead to backprobe the gray/white.

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Customer reply replied 2 years ago
1.01 volts at idle.
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

What is the voltage on the same wire with the sensor unplugged and key on?

What is the resistance to ground on the sensor ground wire?

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Customer reply replied 2 years ago
Source voltage is a constant 5.2v.Ground measured 8 ohmsThe voltage on the grey/white was erratic, from 0.05 to 0.86 volts. Never stopped moving.. Key on. Engine off.
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

Does it set a code with the sensor unplugged?

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Customer reply replied 2 years ago
P0122
Ford Mechanic: sprinkles08, ASE Certified Technician replied 2 years ago

If you jump the signal wire to the 5v wire does it set a P0123? What does the percent show?

What does the percent show with the sensor unplugged?

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sprinkles08
sprinkles08
sprinkles08, ASE Certified Technician
Category: Ford
Satisfied Customers: 23,259
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