Car goes rich when returning to idle. Normal?

[ManBearPig]

In reviewing my datalogs I've started noticing that the car usually goes rich (about .8 lambda) when the throttle is chopped and trans placed in neutral as the car returns to idle. It usually stays rich 2-3 seconds before leveling back out to 1 lamba when it will idle pretty much indefinitely. I've noticed this watching the gauges while driving as well. Ive seen this on the stock tune and my lund tune. Is this written into the tune for some reason? Maybe to cool the cats or something? Just trying to determine if this is a normal behavior. Log showing this attached here

https://datazap.me/u/manbearpig/log-1510154091?log=0&data=1-16&zoom=4082-13030

Thanks

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[Bluemustang]

Pretty sure this is normal but I'll let other experts chime in. Pretty sure it's the car adding fuel after the throttle is cut off. Normal.

 

[jasonstang]

Just some delay in the system I guess.

 

[ManBearPig]

Ive also noticed that when I'm coasting in gear and the car goes into decal fuel shutoff, that as soon as I roll back into the throttle again the car immediately goes rich for a few seconds. For example if I'm slowing down in gear and the car goes to 1.5 lamba (or sometimes even 2.0), as soon as I roll back into the throttle it will immediately go to .8 or so before coming back up to 1. This does not seem to happen if it does not go lean when coasting.


I know the decal fuel cutoff is normal activity, but is it normal for it to go rich? Is this to somehow counter the lean condition previously created?

FWIW I see this on the stock tune as well and both banks do the same thing. Is this intentional?

 

[Zelek]

Stock tunes always run on the richer side in just about any car. Rich = safe.

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