Hi all, in this video we’re going to
discuss how to get the basic idle settings correct. I won’t be
covering how to configure outputs for idle control and wire
them up, because that’s done in a separate video. Just like getting the fuel mixture right, getting
idle control right starts off with having the basic map
correct and then applying closed loop on top to do fine
tuning. So let’s look at the basic factors that go into open
loop idle. Firstly, let’s show where you can find the idle
effort in the software. You can see it on the gauges window,
next to RPM. The RPM field shows the current RPM, the target
RPM and the idle effort (which could be duty cycle, number of
steps or electronic throttle authority). You can also add it
to the monitor window and it also appears in various idle
setup pages. Now, let’s look at the cranking condition. This is
what happens when the engine is stopped, or when it hasn’t yet
reached the cranking RPM threshold, for example 300 RPM. In
this condition, the idle valve is held all the way open to
make the engine easier to start. So the idle effort will be
100% in this condition. Next, let’s consider what happens when the engine
fires. After this happens, the ECU is in the running (as
opposed to cranking) mode. In this mode, the ECU calculates
the idle effort from the following factors:
Base idle effort (which depends on coolant
temperature)
Post-crank idle effort (which depends on
coolant temperature and time)
Additional idle effort for electrical loads,
air conditioner, thermofan, alternator and so on
Closed loop control
Initially, we’ll turn closed loop idle control off.
This enables us to see what the actual settings are doing, as
opposed to how well the ECU can correct it. If we’re setting up the idle from scratch, we should
also set all the idle-up values to zero, and start off with
the base idle effort. This is best done with an engine
starting from cold. Firstly, set the target idle speed against
the coolant temperature; most port injected engines want to
run higher RPM when they are cold to combat the fuel falling
out of suspension at low temperatures. Secondly, as the engine heats up, adjust the base
idle effort in the base duty cycle table against coolant
temperature. Extrapolate past the ends as needed. The other way to do this is to enable closed loop
idle control, and then allow the closed loop function to
settle on the target idle speed. Copy the final idle effort
into the table at each temperature cell as it is reached. Next, you should set up the idle-up for loads. The
procedure for this is to either adjust the additional efforts
so that the target idle is still maintained when the load is
applied, or to allow the closed loop to correct the idle
effort, and take the difference between when the load is
applied and when it is not and copy that into the additional
idle effort. This is also described in the setup article for
the air conditioner and the thermofan. For idle loads which the ECU only knows about via
external inputs, these also need to be wired in and
configured. Generally these are switches which either pull to
ground when they are activated, for example a power steering
pressure switch. For this type of input, select a digital
input that you’re not using, connect the switch to this input,
and select the type as being “power steering” as an example. Another example is a headlight input. Normally this
goes high to 12V when the headlights are on, but is shorted to
ground when they are off. Again this should be connected to a
digital input, and then the input should be selected as an
electrical load, for example electrical load 1. But in this
case because it’s driven high when it’s active, we must select
“active high” in the digital input setting. When any of the electrical inputs, power steering or
air conditioner inputs are active, the ECU will increase the
target idle RPM to the “new target when on” setting in the
idle-up page. If this target is below the target idle speed in
the target idle speed table, it will use the target idle speed
from the table instead (ie, it uses the maximum of the target
idle speed from the table, and the “new target” of any
activated input). The “extra duty – alternator” function is for cars
where the ECU is able to see the alternator field current, for
example if the regulator is built into the ECU rather than the
alternator itself. This is the case with the NB and later MX5
/ Miata, the RX8, 86/FRS/BRZ and the Dodge SRT4 and probably
many others. In this case you can select an input channel for
the field current, enter a maximum and minimum voltage for
that input corresponding to the min and maximum values that
you will see, and minimum / maximum idle efforts for these
conditions. Normally the minimum idle effort would be zero.
The ECU will scale the idle effort linearly between these two
and in practice it works really well; much better than with
digital inputs to select whether different functions on the
car are turned on or not. The final function I wanted to talk about is the
post-crank idle-up. This is a table with coolant temperature
on one axis and time on the other. Time=0 is the time where
the engine actually first fires, and for example 10 represents
10 seconds after the engine has started. This table enables
you to program in a post-crank flare to clear the engine out,
or save it from a stall or whatever is desired on that
particular engine. Note that it will be interpolated between
these points, and the maximium time you can have post-crank
idle for is 300 seconds or 5 minutes (in practice, if you need
it that long you’re probably doing something wrong). Note that
whenever the interpolated value from this table (ie, the extra
idle effort to add due to the post-crank amount) is greater
than 1%, the ECU will not go into closed loop idle. Obviously
during this post-crank flare, it’s going to be above the
target idle speed, and that’s where you want it, so going into
closed loop in this condition is not an option. So the ECU
will stay in open loop until the correction is down to less
than 1%. The only thing I’ll say about setting up the
post-crank idle effort is that sometimes if an engine doesn’t
want to rev up nicely post crank, it’s not because of the idle
effort but it’s instead because of poor fuelling. So if it
doesn’t seem happy and you want it to rev higher or clear
itself up, then you should check the post-crank enrichment
first – try 10% more or 10% less in this table first to see if
it makes a difference. Two final settings – one is the minimum duty cycle.
In most cases you can set this to zero. In some cases, setting
it just below the minimum that you encounter with a hot engine
and no electrical loads can help with idle stability. And on
some idle valves, below a certain duty cycle they actually
start admitting more air, so you need to stay away from that
end of the scale because non-monotonic actuators make Andy
cry. The final setting is “close idle on boost”. In most
turbocharged applications, the air for the idle control valve
will be taken from just before the throttle body, so it really
acts as an idle bypass. However in some cars, even in some OEM
installations like some Toyota 1JZ cars, the idle motor
actually gets its air source from an unpressurised source. So
if the idle valve remains open when the engine is on boost,
air leaks back through the idle valve to the air filter and
creates a boost leak. If you enable this setting, the idle
valve will be closed when the engine is on boost (by closed we
mean set to the minimum duty cycle). In a separate article, we’ll talk about closed loop
idle control.