P0506: Idle Air Control System RPM Lower Than Expected (Meaning, Causes, Fixes)
What P0506 means
At idle, the PCM adjusts how much air gets past the closed throttle to hold a target idle speed while loads like the A/C, heater blower and wipers come and go. Older engines do this with an idle air control (IAC) valve or motor on or near the throttle body; RepairPal notes that after about the 2000 model year, more vehicles moved to drive-by-wire electronic throttle bodies that handle idle air themselves, and OBD-Codes.com says P0506 is often seen on cars with electronic throttle control. P0506 sets when the actual idle speed stays below the PCM's pre-programmed target for a set amount of time. Neither source gives a single RPM threshold; it varies by vehicle. P0507 is the opposite code (idle higher than expected), and P0505 is the general Idle Air Control System code.
Severity: can I keep driving?
Drive with caution, fix soon
Get it checked soon, but the sources disagree on how urgent it is. RepairPal rates P0506 Urgent, since a very low idle can make the engine stall at stop signs or refuse to idle when cold. OBD-Codes.com calls it more of an informational code and says the only thing you'll likely notice is a lower, rougher idle. If the engine stalls when you stop, treat it as urgent, because losing power in traffic is a safety risk. An open code can also fail an OBD2 emissions inspection.
Common symptoms
- Check engine light on (both sources)
- Idle speed lower than normal, often with a rough idle (both sources)
- Engine may not idle when cold (RepairPal)
- Engine may stall at stop signs (RepairPal)
- Erratic idle in some cases (RepairPal)
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Vacuum leak, including intake manifold leaks (both sources)
- Carbon buildup or a dirty or damaged throttle body (both sources)
- Defective or sticking idle air control (IAC) motor (RepairPal)
- Defective power steering pressure switch (RepairPal)
- Faulty PCV (positive crankcase ventilation) valve (OBD-Codes.com)
- Restriction in the intake air path or exhaust (OBD-Codes.com)
- Internal engine problem (OBD-Codes.com)
- Less often, a failed PCM (OBD-Codes.com)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- If other trouble codes are stored, diagnose those first; OBD-Codes.com says P0506 is often a side effect.
- Listen and look for vacuum leaks: cracked or disconnected vacuum hoses, a loose intake boot after the air filter, and intake manifold gaskets.
- Check the PCV valve and its hose.
- Make sure the air filter and intake path aren't blocked.
- Inspect the throttle body for carbon buildup and clean it with throttle body cleaner. RepairPal warns that carbon here is often mistaken for a bad IAC motor. On drive-by-wire throttle bodies, follow your service manual, since some need an idle relearn after cleaning.
- If there are no symptoms other than the code, clear it and see whether it returns, as OBD-Codes.com suggests.
Typical fixes
- Repair vacuum leaks (hoses, intake boot, intake manifold gasket)
- Clean the throttle body and idle air passages
- Replace a faulty PCV valve
- Replace a sticking or failed IAC motor, but only after cleaning the throttle body (RepairPal calls replacing the IAC motor when carbon was the cause a common misdiagnosis)
- Replace a defective power steering pressure switch (RepairPal)
- Repair an intake or exhaust restriction, or an internal engine problem, if testing points there
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- The engine stalls at stops; RepairPal rates P0506 Urgent
- The code returns after cleaning the throttle body and fixing obvious vacuum leaks; RepairPal's shop procedure compares desired versus actual idle in live data under A/C and blower loads, checks fuel trims, EGR and misfires, and lab-scopes the IAC signal
- An internal engine problem or a PCM fault is suspected
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Is P0506 serious?
Usually not by itself, but it can be. OBD-Codes.com calls it more of an informational code, while RepairPal rates it Urgent because the engine can stall at stop signs. If your car stalls, get it fixed right away.
Can I drive with P0506?
If the only sign is a slightly low or rough idle, OBD-Codes.com suggests clearing the code and seeing if it returns. If the engine stalls or won't idle when cold, don't rely on the car in traffic until it's fixed.
Will cleaning the throttle body fix P0506?
Often worth trying first. Both sources list a dirty or carbon-caked throttle body as a cause, and RepairPal says the IAC motor is often replaced when carbon buildup was the real problem.
What's the difference between P0506 and P0507?
P0506 means the idle speed is lower than the PCM expected; P0507 means it's higher than expected. Both are idle control codes, and P0505 is the general Idle Air Control System code.
Why do the sources disagree?
RepairPal rates P0506 Urgent and lists the IAC motor and power steering pressure switch as causes; OBD-Codes.com treats it as mostly informational and instead lists a PCV valve, intake or exhaust restrictions, internal engine problems and the PCM. Both agree on vacuum leaks and the throttle body.
Sources
Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.