PWM IAC Valve Control Mod Kit

This kit provides all the components needed to install the TIP120/121/122 PWM idle valve modification on MegaSquirt V2.2 or V3.0 PCBs. It allows your ECU to drive high-current PWM idle valves directly and is ideal if you're not using the Relay Board’s on/off control or need full idle PWM support.

Note: This mod is not required for PCB v3.57 or MS3-Pro ECUs, which support PWM idle control natively.

Included Components:

• TIP120 / 121 / 122 transistor

• Mica insulator

• Heat sink compound

• 1N4001 flyback diode

• Mounting hardware

V3.0 Installation Notes:

• Do NOT install the small Q4 transistor (from full kit); it’s not suitable for PWM idle valves.

• Mount the TIP transistor on:

  • Spare spot on the heat sink (if available), OR

  • Drill a hole in your case to use it as a heat sink.

• Use the included mica insulator and grease for thermal transfer.

• Jumper R39, and leave D8 and Q20 unpopulated.

• Install the 1N4001 flyback diode across the PWM idle valve terminals (banded end to 12V+).

V2.2 Installation Notes:

• Replace Q5 with the TIP transistor.

• Mount on the case using included insulator and grease.

• No other modifications are necessary.

Wiring:

• Without Relay Board:

  • Idle valve hot wire → Switched 12V+

  • Ground wire → Pin 30 on MegaSquirt DB37

• With Relay Board:

  • Bypass the FIDLE relay with jumper (see guide).

  • Idle valve hot wire → Switched 12V+ (e.g., Fuel Pump power)

  • Ground wire → FIDLE terminal on the Relay Board

This mod allows full control of your PWM idle valve with enhanced reliability and performance.