Idle Air Control System RPM High

What P0507 is actually telling you

The engine is idling higher than the PCM asked for, usually by more than a couple of hundred rpm. The PCM controls idle by moving the throttle or the idle air control valve, and it can see that the engine is running faster than its target despite the correction. That means air is getting in through a path the PCM does not control, or the idle control device is not responding the way it should.

Can you keep driving? Drivable, but not pleasant. A high idle makes the car hard to slow down, can cause a lurch when you shift into gear, and hurts fuel economy. It will not damage anything on its own, so you have time to diagnose it. Do not start swapping the idle valve or the throttle body before you check for a vacuum leak, because that is the more common cause.

The usual suspects, in order

Each cause carries the one test that clears it or confirms it. Work down the list instead of buying parts.

1. A vacuum leak
   Air entering after the throttle plate raises idle exactly the way an open throttle would, and the PCM cannot close a path it does not control. Intake gaskets, PCV hoses, brake booster lines, and cracked intake boots are the usual sources.
   How to check:Compare idle speed and fuel trims before and after pinching off suspect hoses, then smoke test the intake. A leak that only affects idle is a classic vacuum leak.
2. A carboned-up idle air control valve or throttle body
   Carbon on the valve seat or around the throttle plate changes how much air bypasses at idle. On cable-throttle engines the IAC valve sticks; on drive-by-wire engines the plate does not seal the same way once it is dirty.
   How to check:Remove and inspect the valve or throttle body for black deposits. Command the idle control closed with a scan tool and see whether rpm drops as commanded.
3. The idle relearn was never done
   After cleaning a throttle body or disconnecting the battery, the PCM has to relearn the closed-throttle position. Until it does, idle sits high. This is extremely common right after DIY maintenance.
   How to check:Check whether the problem started right after a battery disconnect or throttle cleaning. If it did, run the relearn procedure before you replace anything.
4. A leaking injector seal or an unmetered air path at the manifold
   Injector O-rings that have hardened let air past the seal, which acts like a small vacuum leak that gets worse as the engine warms.
   How to check:Spray a small amount of carb cleaner around the injector bases with the engine idling and listen for a change in rpm. A change means a leaking seal.
5. A load signal the PCM is reacting to
   A power steering pressure switch or an air conditioning request that never clears makes the PCM hold idle up on purpose, because it thinks a load is coming.
   How to check:Watch the load inputs in live data at idle. An input that is active when nothing is running is your answer.

Test it yourself, in this order

Do these before you spend anything on parts. The whole sequence takes about an hour of hands-on time.

What this costs for this engine

Doing it yourself: Throttle body cleaner $10-$15 plus a gasket. IAC valve $40-$150. Vacuum hose $10-$40. Intake gasket set $30-$120 if the leak is at the manifold.

Paying a shop: Diagnosis with a smoke test $80-$150. Idle valve or throttle body service $150-$400. Intake gasket replacement $400-$900 depending on access.

The two cheapest fixes here are also the two most common: cleaning the throttle body properly and running the relearn, and finding a split vacuum hose. Both cost almost nothing and both get skipped in favour of a new valve.

The tool this diagnosis needs

You need bidirectional control so you can command the idle control device and watch the engine respond, and you need the ability to run an idle relearn on drive-by-wire cars. That relearn is the reason a lot of DIY idle repairs never finish: the part is right and the car still idles high because the PCM was never told to relearn.

Notes by make

Work the ranked causes in order rather than replacing parts: run the separating test for the top suspect, rule it out, and move down the list. Most owners who spend money on this code without testing buy the second or third most likely part first.

When to stop and pay a shop

Stop if the relearn procedure requires a factory-level tool your scanner cannot run, if the idle problem started after someone else cleaned the throttle body and the car now needs a dealer relearn, or if the leak is under the intake manifold on a V engine.