I have a 2004 Toyota Corolla and my check engine light is on. The code is P0505: Idle system malfunction. I have replaced the Idle Air Control Sensor and PVC (?) Valve and have no clue what else it could possibly be.

P0505 should be the IAC (Idle Air Control) System Malfunction

Hope this helps

P0505 - Idle Control System Malfunction P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

Error Code: P0505
Fault Location:
Idle Speed Control (ISC) System - Malfunction
Possible Cause:
-Wiring harness.
-Idle speed control (ISC) actuator/Idle air control valve (IAC) valve.
-Throttle valve tight/sticking.
-Engine control module (ECM).

Error Code: P0130
Fault:
Oxygen Sensor (O2S) 1, Bank 1 - Circuit Malfunction
Possible Cause:
Malfunction Indicator Lamp (MIL) Triggered on first occurrence.
-Wiring harness.
-Oxygen sensor (O2S).
-Engine control module (ECM).

Error Code: P0505
Fault:
Idle Speed Control (ISC) System - Malfunction
Possible Cause:
-Wiring harness.
-Idle speed control (ISC) actuator/Idle air control valve (IAC) valve.
-Throttle motor.
-Throttle valve tight/sticking.
-Engine control module (ECM).

Error Code: P0100
Fault Location:
-Mass Air Flow (MAF) Sensor/Volume Air Flow (VAF) Sensor - Circuit --Malfunction
Possible Cause:
-Wiring harness.
-Mass air flow (MAF) sensor.
-Volume air flow (VAF) sensor.
-Engine control module (ECM).

Error Code: P1491
Fault:
Exhaust Gas Recirculation (EGR) Valve Insufficient Lift
Possible Cause:
-Wiring harness.
-EGR Valve.
-ECM

Error Code:P1607
Fault:
-Engine Control Module (ECM)/Powertrain Control Module (PCM)

Error Code: P0966
Location:
-Pressure Control (PC) Solenoid B - Circuit Low
Possible Cause:
-Wiring short to earth.
-Pressure control (PC) solenoid.
-Engine control module (ECM)/Powertrain control module -(PCM)/Transmission control module (TCM) .

per this address "http://www.obd-codes.com/trouble_codes/" p0505 is a "IAC (Idle Air Control) System Malfunction" it gives some good suggestions to look at to find a solution for your problem.

P0505 Idle Control System Malfunction

IACV or Idle Air Control Valve if equipped is malfunctioning.

P0420 Catalyst System Efficiency Below Threshold (Bank #1)
The Catalytic converter is not working up to par in Bank#1.

I think this will point you in the right direction..

P0505 means the whole Idle Control system, not only the IAM. Check all related sensors (i.e. crankshaft sensor). Check with a voltmeter direct at the connector of the IAM if you get any signal. Remove the IAM from the TB, connect him, let someone switch your ignition key to ON. The IAM need to drive in/out for a short time to find the right position. Hold the IAM near a hard part, that they cant drive out completely! If IAM works fine, check the fuel pressure, check and clean your TB ( if not done yet). If that doesn't work, come back again please

does yurs have the idle air control motor if so look into that

Try cleaning the throttle body and idle air control passage. Check for vacuum leaks.

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P1405 Turbo Pressure Sensor Circuit

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P1500 Starter Signal Circuit

P1510 Boost Pressure Control Circuit

P1511 Boost Pressure Low

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P1765 Linear Shift Solenoid Circuit Fault

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