2005 Ford F150 stalls at idle and surges

Recently we came across a 2005 Ford F150 with a 5.4 liter engine that was stalling at idle and had a surging condition at lower engine rpms.  First thought was to pop the hood and look and listen for vacuum leaks which we did as this would be the most common cause of this idle and surging condition.  A preliminary smoke test with our smoke pro revealed no intake manifold or vacuum leaks.  However, upon checking with our scanner revealed two idle related codes.  They were P0505 and P0506.  Below is some information about these two diagnostic trouble codes.

P0505 and P0506 Diagnostic Codes.

P0505 Idle Air Control System Malfunction

Possible Causes:
Air inlet dirty, restricted or the air cleaner is dirty or restricted
IAC valve or solenoid has failed
IAC solenoid control circuit is open or shorted
IAC solenoid power supply circuit is open
PCM has failed.

P0506 Idle Air Control System RPM Lower Than Expected

Possible Causes:
Air inlet dirty, restricted or the air cleaner is dirty or restricted
IAC solenoid or valve or has failed
IAC motor power supply circuit is open
IAC motor control circuit is open or shorted to voltage
Check for a collapsed or loose air inlet duct
PCM has failed

While the definition for these codes refer to the IAC valve or motor as a possible cause, this particular throttle body set up I am talking about is called the drive by wire system that uses an electronic motor on the throttle body.  Ford has engineered a 12 volt two way DC motor onto the side of the throttle body which is controlled directly by the PCM.  There is no IAC motor on this set up.   Instead, the PCM and 12 volt DC motor together are so accurate, the PCM can control the engine idle speed by holding the throttle plate open just enough to allow the right amount of air flow into the engine.  When all goes well, the computer can maintain and control the engine idle speed as needed.  However, that was not the case with this 2005 Ford F-150 and we needed to get to the bottom of it.  While doing some further research, I discovered that Ford released a Technical Service Bulletin for this condition.   It is TSB 08-5-13 for sludging in the throttle body and applies to the 4.6 and 5.4 liter engines.

You can get access to this TSB here

TSB 08-5-13 Vehicle Application:

2004- 2006 F-150 4.6 and 5.4L and 2006 Lincoln Mark LT

This TSB 08-5-13 explains that there is updated strategy for sludge compensation that needs to be programmed into Powertrain control module. Basically, what that means is that the PCM will compensate for this sludge build up inside the throttle body and will adjust things accordingly.  TSB 08-5-13 recommends to reprogram the Powertain Control Module to the latest calibration using (the Ford Factory scanner or IDS) release 53.9 and higher or 54.1 and higher and then after the update, turn the key on and allow the PCM to go through the sludge compensation strategy. Then with the AC off, start the engine and allow it to reach normal operating temperature and check the ETC trim value. If it is 3.0 degrees or greater, replace the Electronic Throttle body (ETC) with the appropriate updated part number.  If the new strategy fixes the concern, no further repair needed.  (Although, I would strongly recommend to clean the throttle body assembly using some throttle body cleaner and a soft wire brush).  However, if reflash/reprogram (and cleaning the throttle body) does not fix the stalling, surging and or idle concern, replace the throttle body with the updated part number.  Here are the new/updated part numbers:

4.6L 6r3z-9e926-aa.  You can get the rebuild kit here, or you can get the complete throttle body assembly here .

5.4L  8l3z-9e926-b  Note: this unit comes with the new TPS sensor.

There are also a few more Technical Service bulletins or TSB’s related to this condition.  For example TSB 12-7-4 and 12-8-1 explain that sometimes the above codes (p0505 and P0506) and or this stalling, idling or surging condition may also exhibit Diagnostic Trouble Codes of P2111 and P2112 (or even a P0121 or P2104) stored in the computer.  They both instruct the technician to clean the throttle body using Ford throttle body cleaner PM-14 and removing all deposits as needed.

TSB 12-7-4 Vehicle Application:

2005-2008 Ford Crown Victoria
2005-2008 Lincoln Town Car
2005-2009 Mustang 2006 Mark LT
2004-2006 F-150
2004-2007 Explorer and F-Super Duty
2005-2008 Grand Marquis
2005-2006 E-Series
2004-2007 Mountaineer
2006 F-53 Motorhome Chassis,
2007 Explorer Sport Trac

TSB 12-8-1 Vehicle application:

Ford 2003-2005 Thunderbird
2003-2006 Lincoln LS
2005-2006 Mustang
2006 Zephyr
2006-2008 Fusion
2005-2006 Navigator
2004-2005 Explorer
2005-2006 Expedition
2006-2008 Mercury Milan
2005-2007 F-150.

Electronic throttle body assembly

P2111 and P2112 Diagnostic Codes.

P2111 Description:  Throttle Control system stuck open

This code is sets when the PCM indicates the throttle plate is at a greater angle that commanded.

Possible causes:
Binding or stuck open throttle body
TAC motor circuits open or shorted
TAC motor fas failed
Damaged PCM

P2112 Description:  Throttle actuator control stuck closed

This code sets when the PCM indicates the throttle plate is lower than commanded.

Possible causes:
Binding or stuck closed
Damaged PCM

Electronic throttle control (ETC) and Electronic throttle body (ETB) overview

On this vehicle, the ETC motor and TPS are two separate components and can each be replaced separately. The motor is mounted on one side of the throttle body while the TPS is mounted on the opposite side.   This style is called the Generation 2 throttle body design and replaces the convention IAC motor, throttle body and 3 wire TPS with a Throttle actuator control (TAC) 12 volt DC two way motor and a 6 wire Throttle position sensor wire (two sensors built into one sensor)  and eliminates the need for a throttle cable.   The 12 volt DC motor is controlled by the vehicles PCM.  Based on my experience, when there is a malfunction with this system, the engine will not accelerate (limp mode) and the “Wrench” light and Malfunction Indicator Lamp will both illuminate.

Checking the throttle body.

The first thing you are going to want to check is the wiring and connector or connections at the throttle body.   Do a good visual inspection to ensure the electronics and wiring are in good shape.   Then you can remove the air intake snorkle and have a look inside.   Inspect the throttle plate and throttle bore for any damage or nicks that could prevent more air from entering the engine than allowed for by the throttle body.   Also, check to ensure that the throttle body is clean and free of debris.   Technical Tip.  When the key is first turned on, the throttle should cycle open and closed, then if the gas pedal is pushed, the throttle should open.   If the throttle plate and TAC motor does not operate properly, it is likely faulty and will need to be replaced after verifying the inputs are correct.

Checking the Throttle Position Sensor signals using a scanner.

You can check the TPS signals using a voltmeter while sitting in the vehicle using a scanner plugged into the 16 pin OBD2 diagnostic connector.  With the key on engine off, check for good reference voltage and ground to the Electronic throttle body.  The first TP signal 1 has a negative slope (increasing angle, decreasing voltage) and TP2 has a positive slope (increasing angle, increasing voltage).  The Electronic Throttle Control Throttle Position Sensor 1 signal should indicate about 4.0 volts at closed throttle and the voltage should steadily decrease as the throttle body plate opens.  The Electronic Throttle Control Throttle Position Sensor 2 value should indicate a reading of about 1.0 volt and steadily increase as the throttle plate opens.  You may want to check these signals a few times opening and closing the throttle plate to ensure a nice smooth even voltage increase or decrease.   This would be just like testing a standard Throttle position sensor.  If the Throttle Position Sensor is not responding while doing this test, be sure to check the circuits/wiring to and from the TPS before replacement.

You can test the throttle body wiring, inputs and signals using a voltmeter if you would like but you would need to gain access to the correct wiring diagram you can first so you know which wires to test and which ones should have what voltage on them.  You can get a factory wiring diagram for this vehicle here.  The key must be on to check the circuit and you would need to back probe the connector at the electronic throttle body connector with it still connected.  On this year, make and model F-150, the Yellow/White wire at pin 2 of the TP sensor connector is the reference wire and it should have 5.0 volts from the main engine computer anytime the key is in the ON position.  Ford calls this circuit ETCREF.  The Pink/Orange wire of the TP sensor is the ground.   Ford calls this the ETCRTN.  Again, you will see both of these acronyms on the factory diagram.  If the TPS fails any of these tests, it is bad and will need to be replaced.  The O.E. part number for the TPS on this vehicle is 6L2Z9B989C.

How to clean the Throttle body.

With the engine off and key removed from the ignition, you can then gain access to the throttle body and open it up to clean it.   You will want to make sure to clean both sides (front and back) of the throttle plate as well as the complete top and bottom of the throttle body.   I would spray some throttle body cleaner on it first using Ford throttle body cleaner PM-14 and let it soak for a bit.  Then use the soft wire brush to clean the inside of the throttle body very good before the cleaner dries.  This applies to both the 4.6L and 5.4 L engines.

Technical Tip:  You can clear the KAM or keep Alive Memory in the computer using certain scanners or scan tools.    This will clear any “learned” memory stored in the computer.  For example, the engine idle RPM.   I am not talking about reflashing or calibrating the main engine computer.   This is simply just a quick fast way to clear the adaptive memory that is stored in the computer and it should always be done after cleaning the electronic throttle body.   This feature is specific to all Ford vehicles.


In the end, this idle condition, stalling, and surging condition along with the two P0505 and P0506 idle codes were caused by deposits in the throttle body leading to less air flow desired which triggered those codes.  On this vehicle with the (5.4 liter engine), we had to replace the throttle body with the updated part number and reflash the PCM with the latest software version available.   The surging and stalling condition are now fixed  and the engine idles smooth.  Customer is happy.  Problem fixed!

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