Yamaha FI Code 37: Idle Speed Control — Fix
On Yamaha motorcycles and scooters, FI fault code 37 means a fault in the idle-speed control system — the fast-idle/ISC valve isn’t controlling idle correctly (often stuck open, giving a high idle after warm-up).
- Applies to
- Yamaha motorcycles
- Est. repair cost
- $20 – $160
- Time to fix
- 30–90 minutes
What it means
Typical causes are a stuck or carbon-fouled ISC/fast-idle valve, a loose/corroded connector, or damaged wiring. This is a generic Yamaha fuel-injection (FI) fault code, so it applies across Yamaha FI models — scooters and underbones like the Mio, NMAX, Aerox, and Sniper, plus YZF-R and MT motorcycles. Yamaha shows the code as a number on the diagnostic/odometer display. Once the fault is repaired and the ECU no longer detects it, the code clears; cycling the ignition (or a Yamaha diagnostic tool) may be needed.
Symptoms
- FI code 37 with warning light on
- High idle after the engine warms up
- Unstable idle or stalling
How to fix it
- 1
Clean the ISC/fast-idle valve
1. Access the idle-control valve on the throttle body. 2. Clean carbon from the valve and passages, then retest idle.
- 2
Inspect wiring and replace
1. Check the connector and wiring. 2. Replace a stuck valve, then clear the code.
Frequently asked questions
Why is my Yamaha idling high with code 37?
The idle-control (fast-idle) valve is stuck open, feeding extra air, so the idle stays high after warm-up. Cleaning or replacing the valve fixes it.
Last updated July 16, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.