Idle speed is higher than the DME's target. On the drive-by-wire 987 there is no separate idle-air valve, so a high idle almost always means unmetered air reaching the engine - a vacuum leak or a dirty throttle body - the same family of causes behind the lean adaptation codes.
SYMPTOMS
- Check-engine light
- High or hanging idle
- Idle doesn't settle after start or on lift-off
LIKELY CAUSES
- Vacuum/intake leak (AOS, boots, manifold O-rings)
- Dirty throttle body / stuck throttle plate
- Failed air-oil separator
- Sticking throttle actuator
DIAGNOSIS STEPS
- Smoke-test the intake for vacuum leaks
- Clean the throttle body and check the plate seals
- Inspect the AOS
- Verify throttle-position live data and adaptation
RELATED PARTS
- Throttle body (drive-by-wire)
- Air-oil separator (AOS)
- Intake boots / vacuum lines