Regarding the posts about what order to do the work, I disagree. There is NOT a direct 2 way communication loop between the IAC itself and the PCM. Makes no difference when the IAC is replaced as long as the battery is disconnected somewhere in the process.
If the battery is not disconnected, there can be a delay as the PCM re-learns the idle trim values. The delay would be in terms of minutes (not days/weeks as others have claimed). In any case, there is a procedure that should be followed regardless. Run the car at idle in park/neutral AC off for at least one FULL minute. Turn the AC on and allow the engine to idle for at least one FULL minute. Do not touch anything during the full minute idle.
In fact, the case could be made for an IAC repair (only) to NOT disconnect the battery but go straight to the idle re-learn procedure. Then the PCM will not have to re-learn all of the other settings.
As far as the far as the black knob is concerned, it is an atmospheric vent.
Really some of the stuff posted sounds almost like voodoo. Disconnecting the battery for 15 minutes should be more than enough. But here is a trick for those out there that think the battery needs to be disconnected for extended periods of time. Disconnect the negative cable from the battery. Jumper the loose negative cable to the positive cable. This will drain away any residual charge in the PCM and the air bag systems.
DTC P1505 is pinpoint test KE20. The first item listed is check for VACUUM LEAKS. The next item listed is stuck open evaporative purge solenoid. Next is the IAC itself.
Since it is so easy, let’s start out with a basic IAC test. Disconnect the IAC electrical connection. If the car immediately stops, the IAC is basically working. If it continues to run, there is a vacuum leak, evaporative purge solenoid stuck open, bad IAC or the wiring to the IAC is bad.
Check the throttle return spring. Is the butterfly valve closing all the way? Has the TB stop screw been adjusted? If it has, this could cause your problem. The TB must close all the way. The system is designed so that virtually all of the idle air is via the IAC.
Do you have access to an ODB2 scan tool to monitor IAC percent? Monitor with the AC on/off. Turn on/off head lights and observe to see if the percent changes. Post the results.
>>>from Ford service manual pinpoint test KE20
KE20 DTC P1506: CHECK FOR VACUUM LEAKS
Key on, engine running.
With the engine at idle, listen for vacuum leaks.
Inspect the entire intake air system from the mass air flow (MAF) sensor to the intake manifold for damage or leaks such as:
Cracked or punctured intake air tube.
Loose or cracked IAC air tubes.
Loose intake air tube at the air cleaner housing or throttle body.
IAC valve or gasket seal.
Intake manifold assembly or gasket seal.
EGR valve gasket seal.
Vacuum supply connectors and hose.
PCV valve, connectors and hose.
Are any leaks detected in the above areas?
(yes)KEY OFF. REPAIR as necessary. (no)KEY OFF. GO to KE21 .
KE21 CHECK EVAP SYSTEM FOR A STUCK OPEN VALVE
Disconnect hoses at EVAP canister purge valve (or VMV).
Connect a hand vacuum pump at the fuel vapor port to EVAP canister at the EVAP canister purge valve (or VMV).
Apply 53 kPa (16 in-Hg) of vacuum to EVAP canister purge valve (or VMV).
Does the EVAP canister purge valve (or VMV) hold vacuum for 20 seconds?
(yes)RECONNECT hoses. GO to KE22 . (no)REPLACE EVAP canister purge valve.
KE22 CHECK IAC VALVE FOR PROPER FUNCTION
Key on, engine running.
Bring engine to normal operating temperature.
Transmission in PARK or NEUTRAL.
Disconnect IAC valve.
Does the rpm drop or engine stall?
(yes)KEY OFF. GO to KE23 . (no)KEY OFF. INSPECT throttle body for damage. REPAIR as necessary. If OK, REPLACE IAC valve. RESET Keep Alive Random Access Memory (RAM). (REFER to Section 2, Powertrain Control Module (PCM) Reset .)
KE23 CHECK IAC CIRCUIT FOR SHORT TO GND IN HARNESS
Note: Refer to the PCM connector pin numbers in the beginning of this Pinpoint Test.
Disconnect scan tool from DLC.
Disconnect PCM.
Measure resistance between IAC circuit at the PCM harness connector and battery negative post.
Is each resistance greater than 10,000 ohms?
(yes)For fast idle symptom currently present:
REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ).
All others:
RESTORE vehicle. GO to KE30.
(no)REPAIR short circuit.
KE30 CHECK IAC SYSTEM FOR INTERMITTENT OPEN OR SHORT
Scan tool connected.
Key on, engine running.
Access IAC PID and RPM PIDs.
With engine at normal operating temperature, accessories off and at idle, the IAC duty cycle must be between 20% and 45%.
Observe the PIDs for an indication of a fault while completing the following at idle:
Lightly tap on IAC valve and wiggle harness connector to simulate road shock.
Grasp the vehicle harness closest to the IAC valve. Shake and bend a small section of the harness from the IAC to the dash panel and from the dash panel to the PCM.
Do the IAC or RPM PIDs suddenly change in value indicating a fault?
Yes No
(yes) ISOLATE fault and REPAIR as necessary.
(no)For idle quality, starting or stalling symptoms currently present:
REPLACE IAC valve.
All others:
Unable to duplicate or identify fault at this time. GO to Z1 .