P0507 Code: Idle Air Control System RPM Higher Than Expected

A P0507 code means the engine idle speed is higher than what the PCM expects — typically 200 or more RPM above the target idle speed. The PCM has a target idle RPM (usually 600-800 RPM depending on the application) and it actively works to maintain it. When the actual RPM consistently exceeds that target despite the PCM trying to pull it down, P0507 sets.

High idle is not just an annoyance. It increases fuel consumption, creates a safety issue (the car wants to creep in gear), and indicates something is introducing extra air or the idle control system is malfunctioning. Let us find the source.

How Idle Speed Control Works

Modern engines control idle speed in one of two ways:

Electronic Throttle Control (Drive-by-Wire)

On most vehicles from about 2005 and newer, the PCM directly controls the throttle blade position through an electric motor. There is no separate idle air control valve — the PCM simply adjusts the throttle blade opening to control idle speed. If idle is too high, the PCM closes the throttle blade further. If it still cannot bring RPM down, it sets P0507.

Idle Air Control Valve (IAC/IACV)

On older vehicles (cable-throttle), a separate IAC valve provides a bypass air path around the closed throttle blade. The PCM controls the IAC to adjust bypass airflow and therefore idle speed. If the IAC is stuck open or there is a bypass air leak, idle goes high.

Common Causes of P0507

Vacuum Leaks

The number one cause. Any unmetered air entering the intake manifold after the throttle body raises idle speed. The PCM does not know about this extra air — it did not command it — so it cannot compensate enough to bring RPM down. Common leak sources:

• Intake manifold gaskets
• Brake booster hose (large vacuum hose — big leak)
• PCV valve hose or grommet
• Cracked intake boot between the throttle body and intake manifold
• Leaking EVAP purge valve (stuck open — fuel vapors and air enter through the purge line)

Dirty Throttle Body

Carbon buildup on the throttle blade and bore creates a gap even when the blade is closed. Air sneaks past the carbon deposits. This is extremely common on direct-injection engines because there is no fuel washing over the intake valves and throttle bore to keep them clean.

IAC Valve Stuck Open (Cable Throttle Vehicles)

The IAC valve plunger or stepper motor is stuck in an open position, allowing too much bypass air. Carbon buildup in the IAC passage is a common cause — the valve cannot close fully because carbon is blocking it.

Incorrect Idle Relearn After Service

If the battery was recently disconnected, the throttle body was cleaned, or the PCM was reset, the idle relearn procedure may not have been completed. The PCM needs to relearn the closed-throttle position and establish a new baseline. Without the relearn, idle can be erratic or too high.

Sticking Throttle Blade (Electronic Throttle)

Carbon or corrosion on the throttle blade pivot points prevents it from closing fully. The motor pushes the blade toward closed, but it sticks slightly open. You will often see the throttle position PID reading 2-5% higher than expected at idle.

Step-by-Step Diagnosis

Step 1: Check Scan Tool Data at Idle

Connect your scan tool and look at these PIDs at idle:

• Engine RPM: How far above target? 100 RPM over is borderline. 300 or more RPM over is significant.
• Throttle position: On electronic throttle, should be 0-2% at idle. If it is 4-8%, the blade may not be closing fully.
• Short-term fuel trim (STFT): If STFT is significantly negative (below -10%), the PCM is pulling fuel to compensate for extra air. This supports a vacuum leak theory.
• Long-term fuel trim (LTFT): High positive LTFT (10% or more) at idle combined with high idle points to a lean condition. Check our P0171 guide for more on fuel trims.
• IAC counts/duty cycle: On IAC-equipped vehicles, look at the IAC position. If the PCM is commanding the IAC fully closed (0% or 0 counts) and the RPM is still high, air is bypassing the IAC — vacuum leak.

Step 2: Listen and Look for Vacuum Leaks

With the engine running, listen for hissing sounds around the intake manifold, throttle body, and vacuum hoses. Use a short length of hose as a stethoscope — put one end to your ear and probe around connections with the other end. A loud hiss in a specific area means you found it.

Step 3: Smoke Test

Introduce smoke into the intake system with the engine off. Seal the intake tube upstream of the throttle body and introduce smoke at about 1 PSI. Watch for smoke escaping from gaskets, hoses, or the brake booster. This is the definitive vacuum leak test.

Step 4: Clean the Throttle Body

Remove the intake tube from the throttle body. With the key on (or using your scan tool to command the throttle open on electronic throttle), look at the blade and bore. If you see black carbon buildup, clean it with throttle body cleaner and a soft brush or rag. Be careful with electronic throttle bodies — do not force the blade open by hand as you can damage the motor gears. Use the scan tool to open it.

Step 5: Perform Idle Relearn

After cleaning the throttle body or any repair that affects idle air, you must perform the idle relearn procedure. This varies by manufacturer:

• Most vehicles: Start the engine, let it reach operating temperature with all accessories off, and let it idle for 5-10 minutes undisturbed. The PCM relearns automatically.
• Nissan/Infiniti: Specific relearn procedure required — turn key on (do not start), wait 3 seconds, pump accelerator 5 times within 5 seconds, wait 7 seconds, hold pedal to floor for 10 seconds, release, start engine. Check the specific service manual.
• GM: Some require a scan tool to perform a throttle body relearn or idle relearn procedure through the special functions menu.

Step 6: Check for a Sticking EVAP Purge Valve

A purge valve stuck open introduces both fuel vapors and air into the intake. Pinch or disconnect the purge valve hose at idle. If the RPM drops immediately, the purge valve is your problem. Replace it.

Common Mistakes

• Cleaning the throttle body without doing an idle relearn. The PCM learned to compensate for the carbon. After cleaning, it is still compensating for carbon that is no longer there. You must relearn.
• Replacing the IAC valve without cleaning the passage. The passage in the throttle body or intake manifold can be just as clogged as the valve itself. Clean the passage when you replace the valve.
• Ignoring the brake booster. A leaking brake booster diaphragm is a large vacuum leak. If the brake pedal feels firm but high idle persists, pull the check valve and hose — if you hear air being sucked into the booster, that is your leak.
• Not checking the EVAP purge valve. This is an overlooked cause of high idle, especially on Honda and Toyota vehicles.

Confirming the Fix

After repair and idle relearn, the RPM should settle at the manufacturer target (check the service manual — usually 650-750 RPM in drive, 700-850 RPM in park/neutral). Clear the code and drive through a complete warm-up cycle. Monitor idle RPM and fuel trims — STFT should be within plus or minus 5% at idle, and the code should not return.

For more on idle control diagnostics, check out the APEX Tech Nation Academy engine performance courses.