Tickovers

[grahamb]

I was at an event earlier in the year, and there was a turbo charged car next to me idling, the engine revs kept climbing, and falling, sounded like someone was sitting in the car blipping the throttle over and over again.

I spoke to the owner, and he said that the ECU was cutting the fuel to make the engine idle, which gave the same effect as someone blipping the throttle.

Why would an ECU need to cut the fuel to make the engine idle ? Is that something supported by all ECU manufacturers?

[Rob Stevens]

If that was an aftermarket ecu, there is a way of creating anti lag without using an extra air valve. You just have the idle set very, very high, like the throttle open 25% then use the ecu to give you some sort of idle by cutting fuel and/or sparks to reduce idle speed to something half way acceptable. DTA has this facility, introduced around V33 - An alternative anti lag feature is available when a valve cannot be fitted. This implements a low RPM limit when the throttle position is below a user defined value. If the engine would naturally idle at say 5000 rpm this will limit the speed when the throttle is closed artificially, providing higher manifold pressure when than would otherwise be the case

[stevieturbo]

Or he could be talking poo, and it's just got a very bad idle and someone told him that lol.

Some ecu's have better idle control than others, and some engines are certainly easier to get a nice idle than others.

And some can be a total nightmare.

Or as Rob says, it could be part of some anti-lag strategy in order to maintain a half sensible idle when it is switched on.

Idle would sound fairly bad though if this was the case

[grahamb]

Yeah it did sound pretty crap. I thought he may have had a servo operating the throttle so had to ask him when the opportunity arose. After 10 mins I just wanted to reach for the isolation switch.

[adamw]

I don’t do much rally stuff but this is not actually anti-lag but just a complimentary part of the strategy. Each Ecu manufacturer has there own term for it but it is usually referred to as “rotational idle”, “cyclic idle” or “cooldown mode” etc.
It was originally for Group N cars where you aren’t allowed to do any of the normally needed antilag mods such as a throttle kicker or bypass valve – so instead they adjust the throttle blade so that it cant fully close to allow the extra air through. When the antilag is active the idle is relatively well controlled by the antilag strategy which is usually an ignition cut and very retarded timing, however when the antilag is turned off you need the “rotational idle” strategy to get the engine speed down to a normal range. Generally a fuel cut is used one cylinder at a time in a rotational pattern – this not only keeps the RPM controlled but the cut cylinders also pump fresh air into the exhaust manifold to cool things down after antilag.