MoTeC Global Forum

Hi guys,

I have an M4 on a 4g63 without any form of idle control with the M4 (no valve installed).
The throttle body utilises wax pallet cold start so cold start is good. It is only the warm idle and stopping at red lights idle that I'm finding difficult to set correctly.

It stalls every now and then etc.
Is it critical to use the P/S switch for some sort of compensation?
Do you have any tips or tricks that I can try to improve this?

Thanks
Baz

Hi Baz,
If the engine dies when it is warm then it is a combination of air, fuel and spark. Unfortunatley idle is a fairly vast subject to go over via forum message.

You can always open the idle screw a little to bring the idle up when warm and then drop some ignition timing to bring the idle rpm back to what you want (don't go below about 5-6 degrees). Then put in a few extra RPM sites in the ignition map, say, every 50-100 RPM below your desired idle RPM. Because you are at fairly low timing due to the throttle being open a bit you can put some more advance in under the idle RPM. Basically if the engine goes to drop RPM it falls on some more timing and does not go down too far.

It can be a bit fiddly to get it right but it will be worth it.

Mark,

It is idling better now after swapping out injectors. I went from 770cc RC Racing to 1000cc Power Enterprise (Denso) injectors and it now idles at lambda 1 whereas the RC's would only idle at .80ish.

I will attempt to do the advised above and see how I go.

bazeng wrote:Mark,

It is idling better now after swapping out injectors. I went from 770cc RC Racing to 1000cc Power Enterprise (Denso) injectors and it now idles at lambda 1 whereas the RC's would only idle at .80ish.

I will attempt to do the advised above and see how I go.

Conventional wisdom would not have suggested that moving to 1000cc injectors would be the way to get improved idle.
There must be something else going on...

I believe that the injectors (RC) are known to have very poor spray patterns at low opening times whereas the Denso injectors were proven to have a good spray pattern at lower opening times and lower pressures.

The conventional wisdom would have been my thought.

Injectors have a mechanical disadvantage in that they have a certain amount of reaction time before the open (called dead time). The also have interesting characteristics when they do not have time to fully open before they close. The dead time of an injector is not necesarily related to its flow capacity, a small injector could have a big dead time.

Spray pattern can affect idle quite badly and I have seen a vast idle improvement from an injector swap before. Trouble is, if I said "change the injectors" as a first step to improving idle it may be met with some resistance.

Like I said, idle is a vast subject.

Also since the M4 cannot control the stock stepper motor setup (4 wire), I will be re wiring the stock ecu to look after all idle duties.

I spoke to Jamie on the phone and he suggests : ref / sync / stepper x4 / possibly water temp is required for the stock ecu to control + aircon request / aircon switch / powersteer switch to have full control.

I'll let you know how it goes.

Thanks guys for the feedback so far.

I would be a bit worried about the factory ECU looking after the idle control if it is only controlling the stepper motor. Most factory ECUs will use ignition timing as well in their idle strategy.

What is the use of the car? Does it have standard injectors and cams?

The car is a street car. It has hks 272/272 cams with 1000cc denso injectors. Currently making 250 front wheel kw. Hopefully 300 plus fwkw once fully tuned.