What rotational idle is for
A lift-off anti-lag system keeps air flowing through the engine when you get off the pedal, often by holding the drive by wire throttle partly open. That's great for keeping the turbo spinning, but with that much air the engine would happily idle at several thousand RPM.
Rotational idle fixes that by cutting cylinders instead of closing off air. The Elite picks cylinders to cut and rotates through them, so no single cylinder sits dead for long. As engine speed climbs toward the limit you set, it cuts more of them. The result is a controlled idle speed with lots of air still passing through, and the choppy, uneven sound people associate with rally cars. Some owners run it just for that sound.
You only need it when the extra air can't be turned off. If your anti-lag air comes through a valve that closes when anti-lag is disarmed, normal idle control can manage on its own.
Arming it with a switch
Enable Rotational Idle Switch on the Wiring tab if you want a physical switch to turn the feature on and off. You can use either an SPI or an AVI.
Switch on an SPI
- Edge: Falling if the switch connects the input to ground when on. Rising if it feeds voltage to the input when on.
- Sensor type: Hall Effect, which is right for any switch.
- Pullup: turn it on when the input needs something to hold it high while the switch is open, such as a switch to ground.
Switch on an AVI
On an AVI you set two thresholds: a Switch On voltage and a Switch Off voltage. Leave a clear gap between them and keep each one well away from the voltage the switch actually sits at, so a bit of electrical noise can't flip the state. For example, if your switch reads close to 5V when on and close to 0V when off, an On threshold around 4V and an Off threshold around 1V gives it plenty of margin.
Settings and our advice
| Setting | What it does | Our advice |
|---|---|---|
| Activating Engine Demand | Rotational idle only works below this pedal (DBW) or throttle (cable) position | Low, so it only acts when you're really off the pedal |
| Idle Valve Position | Idle valve opening while rotational idle is active | Enough to support the anti-lag airflow you want; confirm in logs |
| End RPM | Above this, every cylinder is cut | A little above where the engine would normally idle without anti-lag, adjusted until idle is stable |
| Cut Method | Whether cylinders are cut with fuel or with spark | Injection for most cars (see below) |
| Conditional Activation | Extra conditions that enable or disable the function | Must be enabled if you wired a switch |
Fuel cut or ignition cut?
Injection cut is the usual choice. With no fuel, a cut cylinder just pumps air. Ignition cut keeps the injectors firing, so fuel still flows through the cut cylinders. That's used where the fuel's cooling effect is wanted, but unburnt fuel then ends up in a hot exhaust and turbo, so it's a choice for purpose-built race setups, not something to pick by default.
Conditional activation
This is where you decide when the feature is allowed to run. You can require the switch alone, or combine it with a second condition using And or Or. The second condition is any ECU channel, a comparison (equal to, not equal to, greater than, less than, or the or-equal versions) and a value. A common example is only allowing rotational idle above a certain coolant temperature, so it never runs on a cold engine.
Troubleshooting
| Symptom | Usually |
|---|---|
| Idle hunts or stalls when active | End RPM too low, or too little air for the engine to run on the remaining cylinders |
| Idle still too high | End RPM too high, or the function isn't active (check the switch and conditions) |
| Never activates | Activating Engine Demand set below your real closed-pedal reading, switch configured but Condition Enable off, or wrong edge or thresholds |
| Bangs and pops in the exhaust | Expected to a degree with anti-lag, and much more likely with ignition cut |
Related setup
Rotational idle usually goes hand in hand with anti-lag, drive by wire and idle control. On a Nexus ECU, see rotational idle for NSP.
Rotational idle FAQ
Is rotational idle hard on the engine?
It's a controlled cut, and it rotates so no one cylinder is always the one cut. The bigger stress comes from the anti-lag itself, especially on the turbo and exhaust.
Can I use it without anti-lag?
Yes, but unless you have a reason to hold extra air in at idle, normal idle control gives a smoother result.
