High idle RPM (engine idles too fast)
Engine holds 1500-2000+ RPM instead of a normal 700-900 — causes and OBD-II PIDs to investigate.
High idle means the ECU is commanding extra air/fuel, or the idle air control valve is stuck open.
Causes: (1) vacuum leak past the throttle body — ECU compensates with more RPM and fuel; (2) stuck IACV/EACV; (3) throttle plate slightly open from carbon deposits; (4) IAC solenoid fault in drive-by-wire systems; (5) elevated idle due to A/C or electrical load (normal, but shouldn't exceed 200-300 RPM above baseline).
OBD-II: look for P0507 (idle high), IAC live duty-cycle PID, MAF at idle (abnormally high = vacuum leak), TPS minimum voltage (should be 0.5-0.8V).
First diagnostic steps
- Measure idle RPM when warm (normal 700-900 RPM)
- Check MAF g/s at idle (leak = too high airflow for low RPM)
- Clean throttle body and IACV of carbon deposits
- Inspect vacuum lines downstream of throttle for cracks
- Read IAC Duty Cycle live PID — if 0% but RPM still high = mechanical stuck-open
Likely fault codes
Click a code for detailed description, causes, and diagnostic plan.