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Idle adjustment procedure

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Old 12-10-2009, 08:31 PM   #1
2000StreetRod
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Idle adjustment procedure

I wanted to get my SOHC idle adjusted correctly prior to James Henson making any idle related corrections to my custom tune. There are several threads on the forum describing the 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


Background

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.

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.
Name:  IDLESTOP.JPG
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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) Determine the PCM desired idle speed. Often your tuner will know. If it's not tuned and you don’t have a scanner or data logger to read the parameter then assume 700 rpm. 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.

Last edited by 2000StreetRod; 06-26-2010 at 12:29 PM.
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Old 12-10-2009, 08:33 PM   #2
explorerguy89
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nice guide =] very helpful




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Old 02-13-2010, 04:20 PM   #3
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Did this, worked like a charm, thanks alot!




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Old 11-18-2010, 04:36 PM   #4
dragon6970
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hey can some one help me i have 1986 bronco 11 when i step on the gas my rpms go away then come back any tips
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Old 12-11-2011, 11:31 AM   #5
silv86
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I have a 01 mounty 5.0 that when the IAC valve is unplugged does nothing. Any suggestions? I am experiencing the high idle problems...
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Old 03-09-2012, 12:36 PM   #6
barbaroja
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I thought the IAC was supposed to be fully closed when coolant temp reached operating temperature.
If you suspect of a bad IAC, I would phisycally remove the valve and close the holes to avoid the vacumm leak. Then adjust the screw till it runs stable 700RPMs.

Am I wrong in the IAC operation issue? If the rpms rise as the IAC is connected, that would mean the IAC is not fully closed when in operating temp.

Pleas someone give light. Thanks.
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Old 03-09-2012, 02:30 PM   #7
2000StreetRod
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commanded idle speed

I'm not sure about this but I think the PCM reads the idle speed as reported by the crankshaft position sensor and compares that to a desired idle speed table indexed by engine temperature, inlet air temperature, transmission engaged or not and A/C compressor on or off. It then adjusts the commanded idle speed up or down to achieve the desired speed. If the IAC valve was fully closed then the PCM would not be able to lower the engine speed as needed. However, it probably approaches being closed on a very hot day with the engine hot, the transmission in Neutral/Park, and the A/C compressor off.
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Old 03-10-2012, 12:28 PM   #8
barbaroja
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Ok that makes sense. Upon further research, the recommended 500 rpm with the iac disconnected makes sense. Those 200 rpms are whats left for the PCM to control it. Yesterday I checked my IAC. I am almost sure its bad. However I thought it was a stepper motor, and the steppers I know have 2the coils; this IAC in my 98 sport has only two connectors. I measured it under operation and got qwvokts when I first turned the car switch on. So I am gessing a regular solenoid there.
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Old 12-06-2012, 02:10 PM   #9
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Hello not sure if this is the correct place to post but in need of some serious help. I have been reading for days on here. I have an 05 explorer xlt 4.0l sohc. I was driving it and it started acting like it was getting no gas. All the way to floor would only go about 5 MPH. Codes where 2104 and 2112. Changes Tps. Changed. Plugs and wires. Idle is best ever till you touch. Gas or it sits running for a minute. Now there are 8 codes. P0122, p0223, p2100, p2104,, p2110,, p2111,, p2195. Any help would be such a blessing. Do not have money to take back to Ford again. Sorry if some of the text is crazy trying to post with phone. Thanks in advance and all have a blessed day. Love this site.
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Old 12-06-2012, 03:11 PM   #10
2000StreetRod
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throttle actuator control

P0122 Ford TP Sensor Circuit Low Input
P2100 Ford Throttle Actuator Control Motor Circuit/Open
P2104 Ford Throttle Actuator Control System - Forced Idle
P2110 Ford Throttle Actuator Control Motor Processor
P2111 Ford Throttle Actuator Control System - Stuck Open
P2112 Ford Throttle Actuator Control System - Stuck Closed
P2195 Ford Lack of HO2S-11 Switching, Sensor Indicates Lean

I'm not familiar with the 3rd generation but I think it uses electronic throttle control. From the codes you probably have a problem with the wiring to the actuator motor or the motor itself.
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Old 03-16-2013, 09:45 AM   #11
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Quote:
Originally Posted by dragon6970 View Post
hey can some one help me i have 1986 bronco 11 when i step on the gas my rpms go away then come back any tips
Are you still looking for answer to this problem?

It could be an air leak in a vacuum hose somewhere causing a lean condition when you apply the throttle or it could be too much base timing causing a huge misfire.
The 2nd problem often doesn't cause a backfire but the power will come back with a rush.
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Old 06-24-2013, 10:32 PM   #12
Timmcnamee
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Quote:
Originally Posted by 2000StreetRod View Post
I wanted to get my SOHC idle adjusted correctly prior to James Henson making any idle related corrections to my custom tune. There are several threads on the forum describing the 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


Background

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.

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.
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) Determine the PCM desired idle speed. Often your tuner will know. If it's not tuned and you don’t have a scanner or data logger to read the parameter then assume 700 rpm. 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.
Great write-up. Will this procedure make permanent adjustments to the idle? I got my idle just right using the adjustment screw and then shut it off, turned it back on and it just dropped to the low idle again....
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Old 03-12-2014, 02:19 PM   #13
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'00 302 Explorer 4R70W in an old Volvo. Engine/trans only have abour 11k miles so while old they are not worn out. The only thing that has needed replacing after its 12 year nap in storage has been the injectors. After that everything has run great.

My idle is too high in drive stopped to the point of vibrating. Disconnecting the IAC drops the rpm's about 200 to about 650 - 700 on the tach. Idles perfectly at that. My OBD II reader displays 816 rpm's with or without the IAC so that is an entirely different issue. I have another one and will check with that shortly.

Took the IAC off and cleaned with brake cleaner but it wasn't dirty. No obvious air leaks, no lean codes, LTFT 0.00% with new O2 sensors and about a hundred miles since reset. STFT bouncing around +9% at idle which would seem reasonable.

Is software idle adjustment the next thing?




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Old 03-12-2014, 02:52 PM   #14
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commanded idle speed?

My X3 had a default program loaded in it for some type of Ford (I can't remember which one). One of the monitor parameters was commanded idle speed and another was engine speed. You may want to see what's being commanded. As I recall there are different idle speeds for Park/Neutral, other transmission selections, and A/C compressor on/off. The PCM computes a delta between commanded and actual and then factors the delta into the new commanded. It saves the delta in keep alive memory. Since your idle speed drops when you disconnect the IAC valve connector I assume that the engine is being commanded to the higher speed. If the PCM is reading the correct engine speed then your only option is a software modification of the commanded values.
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Old 03-12-2014, 04:50 PM   #15
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Since you mention A/C I am trying to stretch my little brain around the fact that the PCM is not going to know the status of the A/C as it will be controlled by the 32 year old Volvo controls. The PCM will know rpm, calculate engine load and transmission status and set the IAC accordingly. I think I would make the assumption that those inputs would cause the PCM to attempt to maintain its commanded rpm level without A/C input.

I am going to visit James in Hueytown shortly to address several issues and we will add idle rpm to the list.




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Old 03-12-2014, 07:33 PM   #16
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HVAC function selector switch

The PCM monitors the status of the A/C clutch cycling pressure switch which is in series with the A/C pressure cutoff switch. If the pressure is less than 260 psi the cutoff switch is closed enabling a path to ground. The A/C clutch cycling pressure switch is closed when the pressure is greater than 43.5 psi and open when the pressure is less than 24.5 psi. The PCM reads the switch to adjust the transmission EPC pressure. The PCM also reads via Pin 41 the HVAC function selector switch. If battery voltage is present the PCM assumes the selector is in the MAX A/C, NORM A/C, DEFROST, or DEF/FLR position and activates the A/C compressor via the A/C relay except during WOT. If pin 41 is floating then the A/C compressor is not engaged. What do you have connected to pin 41?
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Old 03-12-2014, 08:11 PM   #17
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Nothing.

The Volvo system manages the compressor based on a temp sensitive contact closure located in the evaporator enclosure. I spliced the Volvo system into the the Ford compressor connector just like the the original operation. Saw no reason to involve the PCM.

Great info that can be applied to other cars.




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