Engine Idles High When Warm — Causes

What's happening

At operating temp, idle should sit around 600–800 RPM (varies by engine). Idle above ~900 means more air is reaching the engine than the ECM expects — usually unmetered air from a vacuum leak — or the idle air control system is stuck open. On drive-by-wire cars, a dirty throttle body or out-of-adjustment throttle position learning will also do it.

You might also notice

• Tach above 900 RPM at a complete stop, warmed up
• Higher idle in gear vs neutral than usual
• Possibly a CEL (P0507 is the textbook code)
• Bad fuel economy

Likely causes (most common first)

1. Vacuum leak (cracked PCV hose, intake boot, manifold gasket, brake booster line)
2. Stuck open IAC valve (older cars)
3. Carbon-buildup keeping the throttle plate from closing fully
4. Throttle position learning lost after a battery disconnect
5. Stuck cruise control servo or cable

What to check first

1. Spray throttle-body cleaner around vacuum lines and intake boot — RPM change = leak found
2. Clean the throttle body if not done in the last 30k miles
3. Drive 15 minutes after a battery disconnect to allow re-learning

Common OBD2 codes for this symptom

Don't have the code yet? Look up your code or read it with AXLY.pro.

Can I keep driving?

Yes. Annoying and bad for economy, but not damaging short-term.

Confirm with the actual code

Symptom-based diagnosis narrows the field — reading the actual stored code finishes the job. AXLY.pro is a free iPhone app that pairs with any Bluetooth OBD2 adapter and reads every stored DTC.