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ECU Master Idle and Transient condition

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I have an interesting issue around idle which is 2 part,

1) During just idle and fan kicking in, seeing interesting lamda figures, not sure why.

So my lambda during idle (after warmup i.e. roughly 80 degrees centigrade) everything seems normal hovering around the target lamda, however when the fans are triggered around 90 degrees, I see erratic behaviour of the lambda numbers where it is struggling to stick to the target it seems

2) When I'm driving the car hard, and I get off throttle, the car (not always) dies, I see a drop in RPM and then shut down

I haven't data logged this condition yet, since I'm still pretty novice and getting to grips with things, but I'm assuming its sudden close of TPS (DBW setup) causing this

Apologies if this seems like a silly question, very new to this so still learning.

Kind regards


When the fans turn on, does the Idle RPM change? if so, it could operating in different cells of your fuel map and those new cells need tuning.

When the fans turn on, what happens to the battery voltage? Has the alternator been energized (sometimes requires a visit of 1500-2500 RPM to activate), and is providing a higher "charging" voltage? If the voltage is dropping, perhaps either your coil dwell is too short for the lower voltage (and you are having mis-fires), or your injector battery compensations (deadtimes) may need correction at the lower voltage.

Use your logging to see if either of those conditions exist.

Hello David,

Thank you for the response.

So had a look at the RPM range,

It was pretty stable, it does fluctuate, but it was consistent with before the fans turned on with regards to battery, there was a slight drop at one point, but the fans were already on at that point, it just dropped to about 13.78V, averaging around 14.2v

I did not tune the car originally myself, however I can definitely look at the injector dead/coil dwell time, looking at the current setup, I am seeing the following,

The values I don't see being a problem perse, but ill definitely double check the numbers based on coils and injectors themselves (Stock VQ35 motor)

The one thing I did not consider before posting (Jotting it down to being new :P) was IAT, as the fans would be pulling warm air into the engine bay, could that not be causing a spike in air temps? I need to go check how the IAT was wired in, but I want to say there wasn't one added onto the intake itself.



Your IAT change is a good idea -- does that change when the lambda readings start swinging?

The lean spikes sure look like misfires (which look lean because there was no combustion to consume the oxygen in the mixture). I notice that the lambda readings get more lean spikes when the Lambda Target drops below 1.0 -- that seems kinda weird -- leads me to believe the injector battery offsets aren't correct.

I would think one way to verify battery offset was correct would be to change the Lambda Target (say from Lambda 1.0 to Lambda 0.90) and if it doesn't get there, reset target to 1.0, modify the battery offset, retune the idle and try changing the target again.

Hello David,

Thanks for the ideas above, im also starting to question the battery offsets (I think it was left as the default table to be honest). The IAT at the time of the spikes didn't really spike, was relatively consistent at 51deg (quite high as the car wasn't moving so warm air just being pulled into engine bay)

I haven't experienced misfire (By experience I mean hear or feel it) but imp definitely going to dig into the battery offsets a bit more. I'm going to try the above and refer back with my findings :)

Thanks for the ideas and time David!