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sprinkles08, ASE Certified Technician
Category: Ford
Satisfied Customers: 22655
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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1999 Ford Explorer 4.0 ohv standard 2wd. Idles at 2200-2500

Customer Question

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: 1 year ago.
Category: Ford
Expert:  sprinkles08 replied 1 year ago.

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?

Customer: replied 1 year ago.
No codes are present or pending. After 45-60 minutes of driving the car behaves properly. No vacuum leaks.
Expert:  sprinkles08 replied 1 year ago.

Are you able to monitor data or actuate the IAC?

Customer: replied 1 year 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.
Expert:  sprinkles08 replied 1 year ago.

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

Customer: replied 1 year 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)
0.11When I disconnect the TPS, it actually runs better.I have two pending codes: 0172 & 0175.
Expert:  sprinkles08 replied 1 year ago.

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

Customer: replied 1 year 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%
Expert:  sprinkles08 replied 1 year ago.

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

Customer: replied 1 year 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%
Expert:  sprinkles08 replied 1 year 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'?

Customer: replied 1 year ago.
No, it does not.
Expert:  sprinkles08 replied 1 year 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.

Customer: replied 1 year ago.
Do I check the voltage between A and B or A and Ground?
Expert:  sprinkles08 replied 1 year ago.

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

Customer: replied 1 year ago.
1.01 volts at idle.
Expert:  sprinkles08 replied 1 year 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?

Customer: replied 1 year 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.
Expert:  sprinkles08 replied 1 year ago.

Does it set a code with the sensor unplugged?

Customer: replied 1 year ago.
Expert:  sprinkles08 replied 1 year 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?