PWM Open Loop

In open-loop mode, the ECU will run the idle valve at the duty looked up from the Coolant based idle duty table (Idle>Open Loop Table). This is sufficient for most race engines, but will lack some of the ability to handle extra ‘idle load’ such as headlights or AC being on - and as a result may need to have a higher than normal idle speed set to compensate. It is typically very good however, and enough to get you to the tuners for fine tuning. If you have problems with Closed Loop tuning, Open loop can be a real help to ‘make do’ until more time can be invested, or knowledge gained, in idle tuning. In the below example, you can see the valve is driven at 25% until the engine starts to warm at which point it tapers down to around 20%.

It is worth noting that the open loop table also forms part of the functionality of Closed Loop idle control, so it should be tuned correctly at all times.