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How to: Idle adjustment procedure

Ck111484

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Hmm, okay, thanks.
I cleaned something that looks very similar to all the pictures of IAC's that I've seen and in pretty much the same location, but someone told me that if you have a 6-pin MAF (which I do), then you have an integrated IAC and there's nothing to clean.
 



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field

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I got a DTC about my TPS after replacing the thermostat housing. Putting in a new TPS didn't help.

This guy -

www.youtube.com/watch?v=FJobCD6y8fk

shows that the problem is seldom the sensor.
He is correct in my case. I got this same DTC before and after installing a new sensor. It is:

P0122 Throttle/Pedal PositionSensor/Switch "A" Circuit Low

He describes how the MAF, MAP and TPS need to agree in orded to have no DTCs.

Anyhow, now I always have a roughly running engine unless I hold the pedal down to keep it above above 1100rpm.

Turning the sensor through it's range while it is out of the intake tube causes some change in the rpm. i.e. I have 5volts to ground where it should be, and a change in rpm while turning the sensor and am mystified why operation isn't normal.

Any further ideas?
 






2000StreetRod

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comments on video

I have a few comments regarding the video:

1. For the Explorer there is a sensor return wire for the TPS that goes to the PCM and is not connected to ground. Voltage measurements should be between the sensor signal wire and the sensor return wire instead of ground.

2. The Explorer has no MAP.

3. The primary sensor for measuring air flow (engine load) is the MAF sensor. The primary function of the TPS is to measure demand (accelerate, decelerate, or maintain current air flow). If the PCM determines the MAF sensor is defective the TPS becomes the primary sensor for calculating load.

4. The typical TPS signal voltage for closed throttle is about 1.0 volts. On 2nd generation Explorers the PCM assumes the closed throttle voltage is the reading when the ignition is turned on. There is no need to adjust the TPS mounting position to achieve a specific closed throttle voltage. The PCM periodically checks for a lower minimum voltage and if found stores that as the new closed throttle voltage. For a scan tool that reads %max instead of voltage the typical closed throttle reading is 18%.

5. Unlike a digital VOM an old style analog VOM provides a continuously updated reading and is more useful for detecting TPS dropouts.

Have you actually tested the signal voltage using back probes? See Ford Explorer - Ranger TPS Test Procedure
 






2000StreetRod

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P0122

According to the Ford OBD System Operations Summary - Model Year 1999, P0122 typically occurs when the PCM measures the TPS output voltage to be less than 0.2 volts. I suggest that you check the TPS electrical connector and wiring for functionality. You may have broken something when replacing the thermostat housing.
 






field

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Greetings 2000StreetRod,

Your descriptions are very elucidating.

Right, my new, but unnecessary since I have to destroy the original one to get the screws out, TPS needed no adjustment.

I found my latest problem to be a vacuum leak since I hadn't sufficiently forced that stiff IAC tube back on it's flexible extension. Curing that eliminated the TPS DTC. So without the youtube guys explanation of the 1 out of 3 sensors (TPS, MAP,MAF) disagreeing with the other 2, I don't know why a vacuum leak would cause the PCM to send a TPS DTC.

Now that I have cooling system pressure for the first time since I owned the SUV, the radiator began to demonstrate it's weakness. So the last month's repairs have cost $655. $185 of which would have been unneeded if the thermostat housing leak wasn't so hard to find and see. However it would have cost about $2500 to have all that done at the shops around here.
Thanks,
field
 






field

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One more thing. Since I have to push the Explorer around in tight turns while it was inoperable, now the power steering wobbles or shakes under stress unlike it ever did before. I suppose that turning without power over stressed the seals?
 






2000StreetRod

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air in power steering fluid

I doubt that turning the wheels without the engine running placed excess pressure on the seals since the power steering pump wasn't turning and generating any pressure. I suspect there is air in the power steering fluid which I think can be purged by turning the wheels from lock to lock with the engine running. Do not hold the wheels locked in either direction for more than a few seconds. If the vehicle is moving forward slowly that will reduce tire scrub. A large, unoccupied parking lot is a good place to try the procedure.
 






field

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Thanks again,
Now the power steering is working fine.
field
 






WildWilly018

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I was curious about proper idle rate. My 2002 explorer sport with the air or heat activated idles at around 500 rpms and drops a bit under when compressor kicks in. One thing is tail pipe rattles at 500 so was thinking it was too low or something. Could you enlighten me on this.
 






2000StreetRod

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stock idle speeds

I looked up the idle speeds in the stock tune for my 2000 Explorer Sport with the 4.0L SOHC V6.

Idle speed neutral = 565
Idle speed drive = 624
Max allowed idle speed drive = 976
MPH for idle control < or = 2
RPM error from desired to begin idle control = 100
Idle speed adder with A/C on in neutral = 0
Idle speed adder with A/C on in drive = 0

There's also a table to vary desired idle speed based on:
Intake air temperature
Engine coolant temperature
Length of time engine has been running in neutral

With the engine warmed up and a fully functional idle speed control there should only be a change in idle speed when shifting between drive and neutral/park. I suggest cleaning or replacing the IAC valve and then checking for intake vacuum leaks.
 






WildWilly018

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idle.

Thanks for the reply. I am sure the truck could use new plugs so will check that also at the same time.
 






albeegood

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There are several threads on the forum describing the idle adjustment process and the following one is very helpful: Idle Air Control Adjustment

There is also the Ford suggested method that is detailed on the LaSota Racing website. Common Idle Issues/Fixes

Below are the stock idle speeds (RPM) for my 2000 SOHC V6 with strategy CDE4.

Idle speed in Neutral (Park) = 656
Idle speed adder with A/C on in Neutral = 0
Idle speed in Drive = 624
Idle speed adder with A/C on in Drive = 0
MPH for idle control = 0 to 2

Idle speed adder for ECT
ECT +RPM
254 . 544
230 . 544
220 . 120
206 .... 0
142 .... 0
100 . 248
<100 248

Idle speed adder for IAT
IAT +RPM
254 .. 48
200 .. 48
190 .... 0
44 ...... 0
34 .... 32
0 .... 232
<0 .. 232

The IAC valve is an electro-mechanical device that is prone to degradation and failure with age. Performing the procedure described below will allow the engine to continue to idle at a reduced engine speed when the IAC valve is no longer functioning correctly. I suggest that you perform the TPS Test Procedure before performing the procedure below.

Your engine should be in reasonably good tune with no vacuum leaks or other problems that would prevent a steady idle.

It is always a good idea to insure the throttle plate does not stick open or closed.

There is no hexagon or slot on the end of the screw that contacts a stop on the throttle body when the throttle plate is closed. Turning the screw opens or closes the throttle plate slightly and acts as a mechanical idle adjustment. The red arrow in the photo below identifies the idle adjustment screw.
View attachment 57300
Thread lock is applied to the screw to prevent movement due to vibration. I decided to replace the screw with a socket (Allen) head cap screw M5-.80 x 20 that I purchased from Lowe's. I lubricated the original screw with WD-40 and proceeded to remove the screw by grasping one end with ViseGrips and rotating the screw. This was a very tedious and time consuming process because the very restricted work space limited each turn to about 30 degrees. When the task was finally completed I installed the replacement cap screw using an Allen wrench. I applied WD-40 to the new cap screw instead of thread lock because it was a tight fit and I did not want it to break!

The vehicle tachometer is not very accurate so I used my X3 Power Flash in the monitor mode to read rpm, desired_idle_rpm, and coolant_temp (engine coolant temperature). I observed that as the coolant_temp increased the desired_idle_rpm decreased gradually to 736 rpm and rpm decreased to 750 rpm with the transmission in Park and the air conditioner compressor not engaged. I experimented with the idle adjustment and the IAC valve connector and learned that the IAC valve controlled idle speed was approximately 200 rpm greater than the idle speed with the IAC valve electrical connector disconnected. I also noticed that actual rpm was approximately 20 rpm greater than desired_idle_rpm. I believe that Ford suggests for a stock engine to adjust the idle speed to 500 rpm with the IAC valve disconnected. Many engine performance modifications detract from a low speed smooth idle. In my case, 550 rpm was much smoother than 500 rpm and resulted in a 750 rpm IAC valve controlled idle. I do not recommend an IAC valve controlled idle speed greater than 850 rpm for vehicles with an automatic transmission. More than that will increase brake wear and transmission fluid temperature and decrease fuel economy. When I selected Drive from Park, the desired_idle_rpm slowly decreased from 736 rpm to 688 rpm. When I switched on the air conditioner the desired_idle_rpm increased.

My revised version of the Ford procedure is as follows:

1) If you have a stock tune use the information above to determine the PCM desired idle speed. If you have a custom tune get the information from your tuner. If you have a custom tune and don't know the value you can read the parameter with a scanner or data logger. This will be your target idle rpm. You do not want the throttle stop adjustment to conflict with the PCM controlled IAC valve.

2) Start the engine and wait for the engine coolant temperature to reach normal operating temperature as indicated on the instrument panel or by OBD monitor. This will take several minutes or longer if a cold start.

3) Disconnect the IAC valve electrical connector. If the engine stops, turn the throttle-stop screw in one full turn, reconnect the IAC valve electrical connector and restart the engine.

4) Repeat step 3 above until the engine continues to run when the IAC valve electrical connector is disconnected.

5) Turn the throttle stop screw to adjust the idle speed to the target rpm minus 200 rpm.

6) Reconnect the IAC valve electrical connector. The engine speed will briefly flare and then settle. Compare the idle rpm to the target rpm. If satisfactory proceed to step 7. Otherwise, disconnect the IAC valve electrical connector, adjust screw accordingly, then reconnect connector and recompare.

7) Turn the ignition Off.

8) Disconnect the negative terminal of the battery cable from the battery. Turn the headlight switch On for 3 minutes then Off and reconnect the battery. This clears stored idle settings and fuel trims.

9) Start the engine and observe the idle speed in Park and in Drive. If satisfactory be comfortable knowing that in the future should the IAC valve fail, the engine will continue to idle but at a lower rpm. If unsatisfactory, disconnect the IAC valve electrical connector, adjust the throttle stop screw as desired and return to step 6.

Notes:

The PCM determines when the engine is at idle by measuring the TPS value when the ignition is switched on and storing it in non-volatile memory. The PCM assumes that the accelerator will not be depressed when switching on the ignition. The PCM periodically checks for a lower TPS value and if one is observed stores that as an updated idle value.

When vehicle speed exceeds 2 MPH (stock tune) and throttle plate is closed PCM will be in dashpot mode instead of idle speed control.

If the brake pedal position switch (BPPS) is not functional the PCM will not unlock the torque converter when the vehicle is stopped and the engine will likely stall.

View attachment 57300
I did this procedure last year and replaced the IAC with a new one and a fuel filter worked just fine. Now this is my problem, in the morning it starts right up. I'll go for a drive engine warms up, if I turn it off go in somewhere or what ever when I come back after 5-10 minutes to start it it won't start on the first try, always on the second try and when it starts it starts but feeling like it's running out of gas. I have to press the gas paddle to bring it to normal idle. PLEASE HELP ...
 






2000StreetRod

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I can think of two possible causes.

The first cause is low fuel pressure. The fuel pump could be weak. The fuel supply check valve could be sticking open. You might try cycling the ignition key between on and off a couple of times before cranking the starter. Each time the ignition is switched from Off to Run the fuel pump is energized for a few seconds. Your 1998 probably has a return type fuel system. The fuel pressure regulator could be defective.

The second cause is a defective engine coolant temperature sensor. If the sensor output is erroneously reporting a cold engine to the PCM when the engine is actually warmed up the fuel mixture will be too rich.
 






albeegood

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I can think of two possible causes.

The first cause is low fuel pressure. The fuel pump could be weak. The fuel supply check valve could be sticking open. You might try cycling the ignition key between on and off a couple of times before cranking the starter. Each time the ignition is switched from Off to Run the fuel pump is energized for a few seconds. Your 1998 probably has a return type fuel system. The fuel pressure regulator could be defective.

The second cause is a defective engine coolant temperature sensor. If the sensor output is erroneously reporting a cold engine to the PCM when the engine is actually warmed up the fuel mixture will be too rich.
Those two areas is what I was thinking on for some reason. I had to replace the thermostat housing because they are plastic and mines was cracked. I noticed it's now leaking some coolant, not much just enough to see it around the housing. Can the temperature sensor be bad and still show it's warm on the Instrument gauge?, mines do show when it warms up. I'm going to see if I can find something on how to troubleshoot those two items. Thx.
 






albeegood

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Those two areas is what I was thinking on for some reason. I had to replace the thermostat housing because they are plastic and mines was cracked. I noticed it's now leaking some coolant, not much just enough to see it around the housing. Can the temperature sensor be bad and still show it's warm on the Instrument gauge?, mines do show when it warms up. I'm going to see if I can find something on how to troubleshoot those two items. Thx.
I can think of two possible causes.

The first cause is low fuel pressure. The fuel pump could be weak. The fuel supply check valve could be sticking open. You might try cycling the ignition key between on and off a couple of times before cranking the starter. Each time the ignition is switched from Off to Run the fuel pump is energized for a few seconds. Your 1998 probably has a return type fuel system. The fuel pressure regulator could be defective.

The second cause is a defective engine coolant temperature sensor. If the sensor output is erroneously reporting a cold engine to the PCM when the engine is actually warmed up the fuel mixture will be too rich.
 






albeegood

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Allow me to say that applying some throttle or just letting it go up on its own it runs good afterwards, can it still be "low fuel pressure" thx.
 






2000StreetRod

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Do you have the OHV or SOHC V6? There are 2 coolant temperature sensors on the SOHC V6. One sends a signal to the instrument cluster and the other sends a signal to the PCM (ECT sensor). The one that matters for how the engine runs is the one connected to the PCM. If the connector to the ECT sensor is loose or the connector wire is broken the PCM should detect that and set a diagnostic trouble code (DTC). Have you checked for any DTCs?

If the fuel supply check valve in the fuel pump assembly is stuck open the fuel pressure will bleed off quickly after shutting off the engine. Then the fuel pressure will be low for the next start because a few seconds is not enough time to repressurize the fuel rail. When the starter motor is cranking the fuel pump runs continuously so there is time to build up pressure. When the engine is running the check valve has no effect on fuel pressure.
 






albeegood

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Do you have the OHV or SOHC V6? There are 2 coolant temperature sensors on the SOHC V6. One sends a signal to the instrument cluster and the other sends a signal to the PCM (ECT sensor). The one that matters for how the engine runs is the one connected to the PCM. If the connector to the ECT sensor is loose or the connector wire is broken the PCM should detect that and set a diagnostic trouble code (DTC). Have you checked for any DTCs?

If the fuel supply check valve in the fuel pump assembly is stuck open the fuel pressure will bleed off quickly after shutting off the engine. Then the fuel pressure will be low for the next start because a few seconds is not enough time to repressurize the fuel rail. When the starter motor is cranking the fuel pump runs continuously so there is time to build up pressure. When the engine is running the check valve has no effect on fuel pressure.
I have the 4.0 SOHC. I did a little reading on a repair manual ( Haynes) and I'm gonna do a little check test to see if I can hear some sound thru the fuel filler hole while key on on ( not start) it says I should hear hissing etc. I'm also gonna see how to check/test the ECT sensor also. Thx y'all so much.
 



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