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 ignition 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 drivability 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 reconnecting 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 carburettor cleaner.
Location
S2
Removal, cleaning and refitting is a 20 minute job. Unplug the loom attachment first. The valve assembly is held in place by four torx screws. The lower two are not visible and have to be located by feel. When the assembly comes free detach the hose. Clean When removed it may be sooty and is cleaned with copious amounts of carburettor cleaner spray (until the fluid runs clear). Fitting is reverse of removal. Screw torque 1.5nm.
Location
"Resetting" the iacv
The IAC Valve postition maybe reset by switching the ignition on disabling the imobiliser and pressing the throttle fully and slowly 5 times, it may also be reset with the Lotus check tool.
This is detailed in section EMN page 14 of the service manual.