Idle Air Control Valve
The Idle Air Control Valve (IACV), or stepper motor, allows the electronic control unit (ECU, a.k.a. MEMS) to regulate the airflow to the engine independently of the driver's throttle input.
When the engine is idling MEMS uses this control (in parallel with igntion timing modulation) to compensate for varying loads that the engine must overcome to maintain the desired idle speed (i.e. friction, electrical load, A/C compressor load etc)
The IACV is also used to control airflow during load changes between positive and negative torque to provide a throttle damping function to improve the driveability characteristics of the vehicle.
- S1 K-Series engined Elises use a Rover IACV (Part No. MLZ100090)
- S2 K-Series engined Elises use a different IACV (Lotus Part No. A117E6069S)
If you are suspiscious that your IACV may be stuck/jammed, you can test it by disconnecting and reconnececting the ECU temperature sender with the car ignition on (but not running). If it can move, you'll hear it chatter as it seeks to a new position when you unplug the sensor.
Fitting and removal
S1
Removal is a simple process and takes less than five minutes. It is held in place by two t20 torx screws although a 3mm allen key will also fit. The lower bolt is slightly harder to get at although easy when the IACV is disconnected from the loom. When removed it may be sooty and should be cleaned with carburetor cleaner.
"Resetting" the iacv
Often people talk about "resetting the iacv" however there is no such procedure, they are probably refering to the Throttle Position Sensor
