P1505

What it means

On a Lincoln, P1505 means the idle air control system has reached the limit of its adaptive learned correction (the 'clip'). The engine control unit is having to command the idle air control valve or throttle to the end of its range to hold the target idle speed, so the idle is being held by a system with no margin left. This usually points to unmetered air, a restricted air path or a fault in the idle control hardware.

Symptoms

• Rough, hunting or unstable idle
• Idle speed too high or too low
• Engine stalls or nearly stalls when coming to a stop or when the air conditioning cuts in
• Hesitation or surging at low speed
• Malfunction indicator lamp on

Possible causes

• Vacuum leak or unmetered air entry (split hose, leaking intake manifold or throttle body gasket, loose intake duct)likely
• Dirty or carbon-clogged throttle body or idle air passageslikely
• Sticking or worn idle air control valve (on models that have one)likely
• Faulty or contaminated mass airflow sensor giving a wrong readingpossible
• Wiring or connector fault in the idle air control circuit, such as corrosion or high resistancepossible
• Leaking PCV system, brake servo hose or EVAP purge valve admitting extra airpossible
• Mechanical engine fault such as worn throttle linkage or incorrect base idle setting (depends on model and engine)rare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting engine temperature, load and idle speed when the code set
2. Check for other fault codes, especially lean or mass airflow codes, and deal with those first as they may be the root cause
3. Visually inspect the intake ducting, vacuum hoses, PCV hose, brake servo hose and manifold joints for splits, loose clips and disconnected pipes
4. Inspect the idle air control valve connector and wiring for corrosion, damage and loose pins, and check resistance and supply against the manufacturer's specification
5. Check the throttle body bore and idle air passages for carbon build-up and check the throttle moves freely
6. With the engine idling, check live data for idle air control duty or position, short and long term fuel trims and airflow reading, and compare with specification
7. Smoke test the intake system to locate small air leaks
8. Check the idle air control valve operation by commanding it with a scan tool and watching the idle speed respond

How to fix

• Repair or replace any leaking vacuum hose, gasket or intake duct found
• Clean the throttle body and idle air passages using a suitable cleaner, taking care with any electronic throttle coating
• Replace the idle air control valve if it is sticking or out of specification
• Repair damaged wiring or connectors in the idle control circuit
• Replace the mass airflow sensor if its readings are implausible after other causes are ruled out
• Clear the code and perform the idle relearn procedure for the specific model once repairs are done, then road test to confirm it does not return

Can I keep driving?

This code for other makes

• P1505BMWIdle Speed Control Valve Closing Solenoid Control Circuit Electrical
• P1505FordIdle Air Control System at Adaptive Clip
• P1505KiaIdle Air Control Valve Opening Coil Voltage Low
• P1505MercuryIdle Air Control System at Adaptive Clip
• P1505OtherIdle Air Control System At Adaptive Clip
• P1505VolkswagenClosed Throttle Position Does Not Close Open Circuit

Nearby codes

• P1504LincolnIntake Air Control Circuit Malfunction
• P1506LincolnIdle Air Control Over Speed Error