How to Test and Clean your Idle Air Controller (IAC)
A frequent problem with older Broncos is a hunting idle. This is where the engine idle fluctuates up and down and doesn't settle into a stable rpm. As we know, the Ford EEC controls engine idle with the help of the IAC (Idle Air Controller), also known as the IAB (Idle Air Bypass), BPA (Bypass Air Valve) or the ISC (Idle Speed Controller). The IAC is an electro-mechanical device that allows air to be bypassed around the Throttle Plate through a bypass channel. EEC controlled idle rpm can be variable depending on whether in neutral or drive gear and there are modifiers for Engine Temperature, Air Conditioning, Power Steering, Alternator Load, etc.
Regarding engine idle, the EEC is programmed as to how much air is able to pass by the closed OEM Throttle Body Plate. Your factory Throttle Body has a Throttle Plate Set Screw that is locked in place with thread locker. This is to prevent you from adjusting your Throttle Body Set Screw which will throw off this programmed airflow scaler value. If you look, your Ford VECI Label specifically states that your idle is not adjustable and is controlled by the EEC.
In addition to the known closed Throttle Body airflow, the EEC commands an additional amount of air through the IAC in order to maintain a given idle rpm. The IAC bypasses air around the Throttle Body Plate by way of a bypass channel. It does this by responding to an EEC pulsed signal opening an internal spring-loaded pintle and valve seat, hence the IAC is limited by it's operational duty cycle. The EEC then monitors the rpm and if the target is not achieved, it will attempt to make additional IAC airflow adjustments up and down looking for the desired idle rpm. The IAC has limitations and may not be able to compensate for modifications such as over/under adjusted throttle plates, aftermarket throttle bodies, camshafts, displacement and so on. These modifications require that the IAC and/or the TB Scaler be reprogrammed in the EEC or a hunting or poor idle condition may exist.
A poor idle can also be caused by excessively rich idle fuelling from an incorrect MAF Sensor calibration, poorly located Oxygen Sensor, out of range ECT Sensor or vacuum leak. With that being said, a frequent cause of poor idle is a dirty or damaged IAC. Cleaning and testing the IAC is a simple process if done correctly. We take for granted that everyone knows how to properly test and clean the IAC but if not done correctly, it can result in even worse idle issues.
The IAC is located on the side of the EFI Throttle Body.
You may or may not want to remove the Air Intake Tube and Throttle Body Cover for better visual and physical access.
Additionally, you may want to remove the entire Throttle Body Assembly to clean it at the same time. If not, the IAC may easily be removed separately for servicing. I can go either way, depending on whether my goal is maintenance or troubleshooting a poor idle.
Here is the IAC Mounted on the side of the Throttle Body. Unplug the harness connector making sure to not break the locking tab.
Before removing the IAC, use a test meter to verify you are getting battery voltage of at least 10.5v. The IAC is a solenoid/valve that runs on battery voltage, not a sensor using 5v reference voltage. Turn the key on/engine off, place your meter on DC Volts and back probe the harness connector wires. To make this easier, I used my wire cutters to quickly fashion terminals out of extra spade connectors. I inserted the modified flat spade ends into the harness connector and then touched the meter probes to the opposite ends.
Using the appropriate size socket, remove the two bolts attaching the IAC to the Throttle Body. Be very careful that you do not drop them as they will be difficult to locate! Be advised there are gaskets and there may be a Idle Air Bypass Spacer between the IAC and the Throttle Body.
Idle Air Adjust Spacer
Allow me to elaborate on the Idle Air Spacer for a moment. Coking on Ford EFI Throttle Blades has been a problem for many years. If the PCV or vent filter clogs, oil tends to back up and accumulate in the Throttle Bore and plate. This is also caused by blow-by from worn piston rings in older engines. The oil becomes a sludgy residue which eventually hardens reducing the expected amount of air that can pass by the closed Throttle Plate. As less air passes by the closed Throttle Plate, the EEC commands the IAC to increase air flow around the Throttle Plate to maintain a good idle. Eventually, the IAC will approach edge of it's operating range. This is the point where the symptoms of poor idle are experienced and Throttle Body/IAC cleaning are indicated.
To alleviate this problem, Ford developed the Idle Air By-pass Service Kit (F2PZ-9F939-A) for EFI Broncos prior to MY1991. The kit includes an Idle Air Adjust Spacer that corrects sludge contamination concerns on the Throttle Blades to the point that Ford no longer covered Throttle Body Cleaning under the 5/50 Emissions Warranty. A secondary benefit is the ability to fine tune closed throttle plate idle air flow without altering the TPS, which has been very popular with Mustang performance builders having idle problems. The Idle Air Bypass Kit was installed by Ford Dealerships under warranty per TSB 91-25-07 and is still available from Ford as well as aftermarket versions from Tomco and eBay.
Beginning in 1991, Ford began using a Sludge Tolerant Throttle Body design which includes a special slick Teflon coating inside the throttle bore. This coating minimizes deposit formation and does not require cleaning or the service kit. The issue is harsh cleaning can remove the sensitive Teflon coating eliminating the protective qualities. These Throttle Bodies can be identified by a black/yellow sticker on the Throttle Body warning against cleaning or adjusting. Please note that this Sludge Tolerant Design does not include the IAC which may still require servicing or replacement.
After removal, lay the IAC on a work surface. Here you can see the valve body, solenoid and connector locations. Also note that on the under side there are two bypass passages that direct air around the Throttle Body Plate.
Next, we will test the IAC Solenoid. We could have done this earlier on the vehicle, but since we will be cleaning the valve it is easier to do now. Place your electrical meter on "Ohms" and touch the two spades on the IAC connector. Resistance should test in either direction. You should have between 7 and 13 ohms. If you are outside of this range, replace the IAC.
Then test the IAC Solenoid for a internal electrical short. With the electrical meter still on "Ohms", test between either spade on the IAC connector and the IAC body. You should see greater than 10,000 ohms or "OL" (Open Loop). If you have continuity, replace the IAC.
If all tests well, we can dissasemble the IAC for cleaning. Many do not (or cannot due to their particular IAC design) and risk damaging the electrical solenoid with cleaning spray. Remove the screws on both sides of the IAC. They will probably be tight to start so be carefull not to strip the heads.
After the screws are removed, pull the solenoid apart from the valve body. Be sure to remember the orientation of the electrical connector.
Be careful as there is an "O"-ring that may be resting on the valve body. It is normally mounted on the solenoid pintle guide and will pull off. Inspect the O-ring for hardening or deterioration and replace if necessary.
Now lay all of the parts out. You should have a valve body, a solenoid, two screws and an o-ring.
Look inside the valve body and you will see the pintle and port seat. This is the target of our cleaning. Push down on the exposed pintle end to see if it moves against the return spring opening and closing the seat and sealing the internal bypass port. This IAC is fairly clean but odds are yours will be full of carbon.
Now, on to the actual cleaning. This is a critical part as the proper cleaner must be used. Never use brake cleaner which can damage internal seals. Only use Throttle Body or Carburator Cleaner.
Spray Throttle Body Cleaner directly into the bypass channel removing any carbon build-up. Keep alternately spraying and draining liquid cleaner until the majority of carbon is removed. Move the pintle end to raise the seat and spray through the internal passageway. Ford recommends that you limit soaking for no longer than 3 minutes. Be careful not to place anything into the passage ways that may nick or scratch the pintle which may create binding. Shake out any remaining cleaner and use compressed air to dry. When you are satisfied, push on the end of the pintle shaft to test for smooth movement and return.
After cleaning is complete, reassemble the IAC. First coat the o-ring with a light coat of motor oil and replace over the solenoid shaft. Then be sure that you have aligned the connector on the solenoid correctly. Reinstall the two screws securely, but do not overtighten or strip the heads.
Now that your IAC has been tested and cleaned, it is time to reinstall it. Although many reuse their IAC gasket, I recommend that you purchase and install a new one as they are inexpensive. Prep the mounting bolt threads by applying anti-seize paste making them easy to remove in the future. To start the IAC mounting bolts, place a single strip of electrical tape between the bolt and socket and press together. This will hold the bolt in the socket giving you an opportunity to start it in the threads. Otherwise, it will likely drop down onto your engine never to be found again. Tighten the bolts to 71-102 inch lbs. being careful not to over torque.
If you have removed and cleaned your Throttle Body, mount the IAC before installing and also use a new Throttle Body gasket. Don't forget to plug in the IAC harness connector!
***All looks great at this point, but we are definitely not done. Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that the KAM (Keep Alive Memory) be cleared. This provides an Idle Relearn which is crucial to achieving a smooth idle because it permits the IAC solenoid to be brought back within its normal operating range. Disconnect your battery for at least 5 minutes to clear previously learned Idle Air Trim values. Then with all accessories off, start your engine and allow it to idle for at least 15 minutes to relearn the idle strategy. You will slowly hear your idle improve so do not be overly concerned at the beginning. That is, unless you did not test and reinstalled a bad IAC...
One final note, some IACs may be of a vented type having a vent and filter used to equalize pressure within the valve. This type of IAC has a solenoid and valve body which are permanently attached and cannot be separated. These are generally found on OEM Sludge Resistant Throttle Body Assemblies on 1991+ Broncos. It is said that this type cannot be safely cleaned without damaging the solenoid, though many continue to carefully clean them when necessary. Hold the IAC vertically with the Solenoid toward the top to minimize spray cleaner intrusion into the electrical housing. Also ensure the vent port is clear by removing the vent cap and directing spray cleaner through the vent port. Otherwise, this type of IAC should electrically test the same as the non-vented type.
The original vented IAC below from my 1994 F250 tested good and was cleaned. I reinstalled it and it still would not control idle. I again removed the IAC and noted that the pintle was very difficult to move. After replacement with a new Motorcraft IAC, I cleared the KAM and subsequently found a perfectly controlled idle. The point being sometimes an old IAC simply needs to replaced due to mechanical wear, even though it electrically tests good.
Now you are done and it's time for a beer! Not so hard, was it? :beer
A frequent problem with older Broncos is a hunting idle. This is where the engine idle fluctuates up and down and doesn't settle into a stable rpm. As we know, the Ford EEC controls engine idle with the help of the IAC (Idle Air Controller), also known as the IAB (Idle Air Bypass), BPA (Bypass Air Valve) or the ISC (Idle Speed Controller). The IAC is an electro-mechanical device that allows air to be bypassed around the Throttle Plate through a bypass channel. EEC controlled idle rpm can be variable depending on whether in neutral or drive gear and there are modifiers for Engine Temperature, Air Conditioning, Power Steering, Alternator Load, etc.
Regarding engine idle, the EEC is programmed as to how much air is able to pass by the closed OEM Throttle Body Plate. Your factory Throttle Body has a Throttle Plate Set Screw that is locked in place with thread locker. This is to prevent you from adjusting your Throttle Body Set Screw which will throw off this programmed airflow scaler value. If you look, your Ford VECI Label specifically states that your idle is not adjustable and is controlled by the EEC.
In addition to the known closed Throttle Body airflow, the EEC commands an additional amount of air through the IAC in order to maintain a given idle rpm. The IAC bypasses air around the Throttle Body Plate by way of a bypass channel. It does this by responding to an EEC pulsed signal opening an internal spring-loaded pintle and valve seat, hence the IAC is limited by it's operational duty cycle. The EEC then monitors the rpm and if the target is not achieved, it will attempt to make additional IAC airflow adjustments up and down looking for the desired idle rpm. The IAC has limitations and may not be able to compensate for modifications such as over/under adjusted throttle plates, aftermarket throttle bodies, camshafts, displacement and so on. These modifications require that the IAC and/or the TB Scaler be reprogrammed in the EEC or a hunting or poor idle condition may exist.
A poor idle can also be caused by excessively rich idle fuelling from an incorrect MAF Sensor calibration, poorly located Oxygen Sensor, out of range ECT Sensor or vacuum leak. With that being said, a frequent cause of poor idle is a dirty or damaged IAC. Cleaning and testing the IAC is a simple process if done correctly. We take for granted that everyone knows how to properly test and clean the IAC but if not done correctly, it can result in even worse idle issues.
The IAC is located on the side of the EFI Throttle Body.
You may or may not want to remove the Air Intake Tube and Throttle Body Cover for better visual and physical access.
Additionally, you may want to remove the entire Throttle Body Assembly to clean it at the same time. If not, the IAC may easily be removed separately for servicing. I can go either way, depending on whether my goal is maintenance or troubleshooting a poor idle.
Here is the IAC Mounted on the side of the Throttle Body. Unplug the harness connector making sure to not break the locking tab.
Before removing the IAC, use a test meter to verify you are getting battery voltage of at least 10.5v. The IAC is a solenoid/valve that runs on battery voltage, not a sensor using 5v reference voltage. Turn the key on/engine off, place your meter on DC Volts and back probe the harness connector wires. To make this easier, I used my wire cutters to quickly fashion terminals out of extra spade connectors. I inserted the modified flat spade ends into the harness connector and then touched the meter probes to the opposite ends.
Using the appropriate size socket, remove the two bolts attaching the IAC to the Throttle Body. Be very careful that you do not drop them as they will be difficult to locate! Be advised there are gaskets and there may be a Idle Air Bypass Spacer between the IAC and the Throttle Body.
Idle Air Adjust Spacer
Allow me to elaborate on the Idle Air Spacer for a moment. Coking on Ford EFI Throttle Blades has been a problem for many years. If the PCV or vent filter clogs, oil tends to back up and accumulate in the Throttle Bore and plate. This is also caused by blow-by from worn piston rings in older engines. The oil becomes a sludgy residue which eventually hardens reducing the expected amount of air that can pass by the closed Throttle Plate. As less air passes by the closed Throttle Plate, the EEC commands the IAC to increase air flow around the Throttle Plate to maintain a good idle. Eventually, the IAC will approach edge of it's operating range. This is the point where the symptoms of poor idle are experienced and Throttle Body/IAC cleaning are indicated.
To alleviate this problem, Ford developed the Idle Air By-pass Service Kit (F2PZ-9F939-A) for EFI Broncos prior to MY1991. The kit includes an Idle Air Adjust Spacer that corrects sludge contamination concerns on the Throttle Blades to the point that Ford no longer covered Throttle Body Cleaning under the 5/50 Emissions Warranty. A secondary benefit is the ability to fine tune closed throttle plate idle air flow without altering the TPS, which has been very popular with Mustang performance builders having idle problems. The Idle Air Bypass Kit was installed by Ford Dealerships under warranty per TSB 91-25-07 and is still available from Ford as well as aftermarket versions from Tomco and eBay.
Beginning in 1991, Ford began using a Sludge Tolerant Throttle Body design which includes a special slick Teflon coating inside the throttle bore. This coating minimizes deposit formation and does not require cleaning or the service kit. The issue is harsh cleaning can remove the sensitive Teflon coating eliminating the protective qualities. These Throttle Bodies can be identified by a black/yellow sticker on the Throttle Body warning against cleaning or adjusting. Please note that this Sludge Tolerant Design does not include the IAC which may still require servicing or replacement.
After removal, lay the IAC on a work surface. Here you can see the valve body, solenoid and connector locations. Also note that on the under side there are two bypass passages that direct air around the Throttle Body Plate.
Next, we will test the IAC Solenoid. We could have done this earlier on the vehicle, but since we will be cleaning the valve it is easier to do now. Place your electrical meter on "Ohms" and touch the two spades on the IAC connector. Resistance should test in either direction. You should have between 7 and 13 ohms. If you are outside of this range, replace the IAC.
Then test the IAC Solenoid for a internal electrical short. With the electrical meter still on "Ohms", test between either spade on the IAC connector and the IAC body. You should see greater than 10,000 ohms or "OL" (Open Loop). If you have continuity, replace the IAC.
If all tests well, we can dissasemble the IAC for cleaning. Many do not (or cannot due to their particular IAC design) and risk damaging the electrical solenoid with cleaning spray. Remove the screws on both sides of the IAC. They will probably be tight to start so be carefull not to strip the heads.
After the screws are removed, pull the solenoid apart from the valve body. Be sure to remember the orientation of the electrical connector.
Be careful as there is an "O"-ring that may be resting on the valve body. It is normally mounted on the solenoid pintle guide and will pull off. Inspect the O-ring for hardening or deterioration and replace if necessary.
Now lay all of the parts out. You should have a valve body, a solenoid, two screws and an o-ring.
Look inside the valve body and you will see the pintle and port seat. This is the target of our cleaning. Push down on the exposed pintle end to see if it moves against the return spring opening and closing the seat and sealing the internal bypass port. This IAC is fairly clean but odds are yours will be full of carbon.
Now, on to the actual cleaning. This is a critical part as the proper cleaner must be used. Never use brake cleaner which can damage internal seals. Only use Throttle Body or Carburator Cleaner.
Spray Throttle Body Cleaner directly into the bypass channel removing any carbon build-up. Keep alternately spraying and draining liquid cleaner until the majority of carbon is removed. Move the pintle end to raise the seat and spray through the internal passageway. Ford recommends that you limit soaking for no longer than 3 minutes. Be careful not to place anything into the passage ways that may nick or scratch the pintle which may create binding. Shake out any remaining cleaner and use compressed air to dry. When you are satisfied, push on the end of the pintle shaft to test for smooth movement and return.
After cleaning is complete, reassemble the IAC. First coat the o-ring with a light coat of motor oil and replace over the solenoid shaft. Then be sure that you have aligned the connector on the solenoid correctly. Reinstall the two screws securely, but do not overtighten or strip the heads.
Now that your IAC has been tested and cleaned, it is time to reinstall it. Although many reuse their IAC gasket, I recommend that you purchase and install a new one as they are inexpensive. Prep the mounting bolt threads by applying anti-seize paste making them easy to remove in the future. To start the IAC mounting bolts, place a single strip of electrical tape between the bolt and socket and press together. This will hold the bolt in the socket giving you an opportunity to start it in the threads. Otherwise, it will likely drop down onto your engine never to be found again. Tighten the bolts to 71-102 inch lbs. being careful not to over torque.
If you have removed and cleaned your Throttle Body, mount the IAC before installing and also use a new Throttle Body gasket. Don't forget to plug in the IAC harness connector!
***All looks great at this point, but we are definitely not done. Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that the KAM (Keep Alive Memory) be cleared. This provides an Idle Relearn which is crucial to achieving a smooth idle because it permits the IAC solenoid to be brought back within its normal operating range. Disconnect your battery for at least 5 minutes to clear previously learned Idle Air Trim values. Then with all accessories off, start your engine and allow it to idle for at least 15 minutes to relearn the idle strategy. You will slowly hear your idle improve so do not be overly concerned at the beginning. That is, unless you did not test and reinstalled a bad IAC...
One final note, some IACs may be of a vented type having a vent and filter used to equalize pressure within the valve. This type of IAC has a solenoid and valve body which are permanently attached and cannot be separated. These are generally found on OEM Sludge Resistant Throttle Body Assemblies on 1991+ Broncos. It is said that this type cannot be safely cleaned without damaging the solenoid, though many continue to carefully clean them when necessary. Hold the IAC vertically with the Solenoid toward the top to minimize spray cleaner intrusion into the electrical housing. Also ensure the vent port is clear by removing the vent cap and directing spray cleaner through the vent port. Otherwise, this type of IAC should electrically test the same as the non-vented type.
The original vented IAC below from my 1994 F250 tested good and was cleaned. I reinstalled it and it still would not control idle. I again removed the IAC and noted that the pintle was very difficult to move. After replacement with a new Motorcraft IAC, I cleared the KAM and subsequently found a perfectly controlled idle. The point being sometimes an old IAC simply needs to replaced due to mechanical wear, even though it electrically tests good.
Now you are done and it's time for a beer! Not so hard, was it? :beer