Creating steam coasting effect

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Having installed a loksound V4 sound chip in my Garratt I am very leased with the result. I have yet to fine tune some of the CVs but would like some advice on creating the coasting effect on a steam loco especially as it drifts to a halt. This is my first steam sound decoder and on my diesels just easing the throttle slightly creates coasting. My Garratt will not go above about a scale 40 mph and I will set CVs 3 & 4 for slow acceleration and even slower deceleration.

Are there any tips regarding CV setting that will create the coasting effect whilst running and more importantly when drifting to a halt.

Thanks in anticipation