Car conks out when coming to a stop

[Bruce Hazell]

Hi all...I have a 91 ZRF-1..modified somewhat many years ago by Haibeck so his chip is in there:}
Anyway over the years but more recently when coming to a quick stop or slow down with clutch disengaged quite often the revs bounce down from just under 1,000 which seems to be normal idle speed to around 800. Sometimes bounces back up to 1,000 or if not conks out. Restarts ok.

Can be a little dangerous if turning as power steering of course dies not to mention its embarrassing as hell at a set of lights. If I turn the AC on which cause the revs to drop a tad at idle it is almost guaranteed to conk out as coming to a stop.
When just sitting idiling in my driveway this does not happen AC or no AC.
Any thoughts as to what may be the cause or the solution.
Back in the day would just turn a screw and increase the idle..hahaha!