Originally Posted by dave-o

I changed the battery 3 days ago. Ever sense i changed it, the CEL light has been on and my a/c is not cooling as well as it should, esp. taking a LONG time to blow moderately cool air. any ideas?

Originally Posted by '04 PCED

P0506 - Idle Air Control System RPM lower than expected
This DTC is set when the PCM detects engine idle speed that is less than the desired rpm. Possible causes:
- IAC circuit open
- Air inlet is plugged
- Damaged or incorrect IAC valve
- IAC valve stuck closed
- VPWR to IAC solenoid open
- IAC circuit shorted to PWR
- Damaged PCM
Disconnect IAC valve and look for no change in engine rpm as an indication of a stuck or damaged valve.

KE2 DTCS P0505, P0506, P0511, P1504 OR P1507: (OR STARTS ONLY AT PART THROTTLE) CHECK VPWR VOLTAGE TO IAC VALVE
Note: If EGR DTC P0402 was output during Self-Test, diagnose it first before continuing with this Pinpoint Test.

IAC Actuator connector disconnected.
Key ON Engine OFF.
Measure the Voltage between:

( + )IAC Actuator Connector, Harness Side ( - )Vehicle battery
VPWR - Pin 1 Negative post

Is the Voltage above 10.5 V?
Yes - KEY OFF. GO to KE3 .
No - KEY OFF. REPAIR open circuit.

KE3 CHECK RESISTANCE OF IAC VALVE
IAC Actuator connector disconnected.
Measure the Resistance between:

( + )IAC Actuator Connector, Component Side ( - )IAC Actuator Connector, Component Side
IAC - Pin 2 VPWR - Pin 1

Is the Resistance between 6 Ohm - 15 Ohm?
Yes - GO to KE4 .
No - INSTALL a new IAC Valve.

KE4 CHECK THE IAC VALVE FOR AN INTERNAL SHORT TO THE IAC CASE
Measure the Resistance between:

( + )IAC Actuator Connector, Component Side ( - )IAC Actuator Connector, Component Side
IAC - Pin 2 IAC Case

Is the Resistance above 10 KOhm?
Yes - GO to KE5 .
No - INSTALL a new IAC actuator.

KE5 CHECK AIR INLET FOR PLUGGING OR STUCK IAC PINTLE
INSPECT the entire intake air system for debris, blockage or other damage.
Remove and inspect the IAC valve and check the pintle movement. Check air tubes (if equipped) for blockage or damage.
Remove and inspect the air cleaner element for excessive dirt.
Is the IAC valve and intake air system ok?
Yes - Restore the inlet air system. GO to KE6 .
No - INSTALL a new IAC valve or repair air inlet as necessary.

KE6 CHECK FOR INLET AIR LEAKS
Key ON Engine RUN.
With the engine running at idle, listen for vacuum leaks.
INSPECT entire air intake system from the mass air flow (MAF) sensor to the intake manifold for leaks such as:
Damaged or loose IAC air tubes.
Cracked or punctured intake air tube.
Loose intake air tube at air cleaner housing or throttle body.
IAC valve or gasket seal.
EGR valve gasket seal.
Vacuum supply connector and hose.
PCV valve, connectors and hoses.
Are any leaks detected in the above areas?
Yes - KEY OFF. Repair as necessary.
No - KEY OFF. GO to KE7 .

KE7 CHECK THE IAC CIRCUIT FOR OPEN IN HARNESS
Note: REFER to the PCM connector pin numbers in the beginning of this pinpoint test.

IAC Actuator connector disconnected.
PCM connector disconnected.
Measure the Resistance between:

( + )IAC Actuator Connector, Harness Side ( - )PCM Connector, Harness Side
IAC - Pin 2 IAC

Is the Resistance below 5 Ohm?
Yes - GO to KE8 .
No - REPAIR open circuit.

KE8 CHECK IAC CIRCUIT FOR SHORT TO POWER IN HARNESS
Key ON Engine OFF.
Measure the Voltage between:

( + )PCM Connector, Harness Side ( - )Vehicle battery
IAC Negative post

Is the Voltage below 1 V?
Yes - KEY OFF. GO to KE9 .
No - KEY OFF. REPAIR short circuit.

KE9 CHECK IAC CIRCUIT FOR SHORT TO GROUND IN HARNESS
Scan tool connector disconnected.
Measure the Resistance between:

( + )PCM Connector, Harness Side ( - )
IAC Ground

Is the Resistance above 10 KOhm?
Yes - GO to KE10 .
No - REPAIR short circuit.

KE10 VERIFY DTC
Is DTC P0511 or P1504 present in Continuous Memory or from the KOER Self-Test?
Yes - INSTALL a new PCM.
No - GO to KE11 .

KE11 CHECK THE IAC SIGNAL FROM THE PCM
PCM connector connected.
IAC Actuator connector connected.
Note: If stalling occurs, place a shim under the hard stop screw to maintain idle conditions.

Key ON Engine RUN.
Access the PCM-RPM PID using a scan tool.
Access the PCM-IAC PID using a scan tool.
With the engine at normal operating temperature, closed throttle and all accessories OFF, the IAC duty cycle should be between approximately 22 and 65 percent.
Slowly increase the engine speed to 3000RPM and return to closed throttle (Note: If closed throttle RPM is significantly higher than normal, ignore this step).
Is the Duty Cycle between 22% - 65%?
Yes - GO to KE12 .
No - KEY OFF. INSTALL a new IAC actuator.

KE12 VERIFY DTC
Is DTC P0506, P0511, P1504 or P1507 present in Continuous Memory or from Self-Test?
Yes - GO to KE18 .
No - KEY OFF.
INSPECT throttle body for damage. Repair as necessary. If ok, install a new IAC actuator.
RESET Keep Alive Random Access Memory (RAM) (REFER to Section 2, Powertrain Control Module (PCM) Reset).