spark scatter...what's normal

[going4speed]

My car has a very lopey idle. Stock cam etc.

Got MPScan to work and looking at a bunch of graphs and everything seems normal.

The spark scatter gage jumps all over the place like crazy. I dont know if that's normal. It will jump from one side of the gage to the other.

Thoughts?

[zin]

You might be seeing the ECU trying to control the idle, and failing, is the IAC maxed out or stuck in one position?

The big question is what else is wrong, or was recently changed? Are there vacuum leaks/ broken plastic lines?

Mike

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You might be seeing the ECU trying to control the idle, and failing, is the IAC maxed out or stuck in one position?

The big question is what else is wrong, or was recently changed? Are there vacuum leaks/ broken plastic lines?

Mike

[going4speed]

IAC sits around 26 but there is movement on that number just not much.

[ShelGame]

That's normal. Spark scatter values can be positive timing or negative.

Our ECU's try to control the idle speed with spark and fuel primarily. IAC adjustments are a 'last resort' so to speak. The reason being, that with a Speed-Density system, any change in MAP (due to the IAC opening / closing) would get a corresponding PW change for 'transient' fuel.

A ported head, or higher lift/overlap cam will have an effect on the idle quality, and the spark scatter control would need to be tuned to give a good idle. I don't really have any experience tuning the idle control. It has to be a hands-on car-by-car process to get it right.

[Aries_Turbo]

How's the fuel mix/adaptives at idle. Fueling has a huge impact on idle.

[going4speed]

What are adaptives called in the list of choices for gauges?