Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Idle Control System: Notes
Idle speed is controlled by ECU through AAC valve and Fast Idle Control Device (FICD) valve on G20 and M30. ECU controls idle speed components based upon signals received from various input devices. If idle speed components test correctly but idle speed is not being regulated properly, check input signals to ECU. See IDLE SPEED SYSTEM INPUT SIGNALS table.
On Q45, fast idle is controlled by fast idle cam on non-traction control system equipped vehicles and air cut valve on traction control system equipped vehicles. Engine coolant temperature changes volume of wax element to control amount of air by-passing secondary throttle valve. As engine warms, by-pass air is reduced, reducing idle speed.
| Application | Model Usage | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| A/C Clutch Signal (1) | G20, M30 & Q45 | ||||||||
| Airflow Meter | Q45 | ||||||||
| Battery Voltage | G20, M30 & Q45 | ||||||||
| Crank Angle Sensor | G20, M30 & Q45 | ||||||||
| Engine (Coolant) Temperature | G20, M30 & Q45 | ||||||||
| Ignition (START) Switch | G20, M30 & Q45 | ||||||||
| Neutral Switch | (2) G20 | ||||||||
| Park/Neutral (Inhibitor) Switch | G20, (3) M30 & (4) Q45 | ||||||||
| Power Steering Pressure Switch | G20, M30 & Q45 | ||||||||
| Throttle Position Sensor | G20, M30 & Q45 | ||||||||
| Throttle (Idle) Switch | M30 & Q45 | ||||||||
| Vehicle Speed Sensor | G20, M30 & Q45 | ||||||||
|
|||||||||
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.