Sensors & outputs Actuator
Stepper idle
GM 4-wire IAC · output · Actuator
Bipolar 4-wire stepper. Coil A on ETB 1±, coil B on ETB 2±. Cable-throttle LS1, many Toyotas, many BMWs. Cannot run on the same Race Core as an electronic throttle.
Typical parts: GM LS1 4-wire IAC; Toyota 4-wire stepper; Ford 4-wire IAC
Warning — XOR with ETB. Same two H-bridges. Pick stepper idle or electronic throttle.
Device pinout
Looking into the valve. Four cavities in a square; letters are stamped.
- Connector: GM 4-way square on the valve
- Layout (looking into the part): A · B / D · C
| Device pin | Function | Type | Race Core | TunerStudio |
|---|---|---|---|---|
| A | Coil A | H-bridge | B7 | ETB 1+ |
| B | Coil A return | H-bridge | B6 | ETB 1− |
| C | Coil B | H-bridge | B15 | ETB 2+ |
| D | Coil B return | H-bridge | B8 | ETB 2− |
Wiring notes
- If idle runs away from the target (valve winds the wrong way), swap one coil pair — A with B, or C with D. Do not swap both.
- 2-wire PWM idle valves are a low-side plus switched 12 V, not this page. Use a spare low-side, not the H-bridge.
- Pintle and seat must be clean. A carboned IAC looks like a PID that will not settle.
- Home the stepper in TunerStudio before first start so the pintle is not driven into the seat at 100 %.
Failure modes
- Idle runs away from the target: one coil pair is reversed. Swap A with B, or C with D. Do not swap both.
- Pintle hammers the seat: the stepper was not homed before the first start.
- Valve never moves and the ECU reports no fault: it is a 2-wire PWM idle valve on the H-bridge pins. That valve wants a spare low-side and switched 12 V.