Slow returning to idle speed

My '92 Metro is very slow to return to idle speed after coming to a stop. The car does not have a tach, but idles somewhat high, then slowly "sinks" to idle speed (800 RPM). The idle seems somewhat rough at times, almost like the speed has actually dropped below the set idle speed. This only happens on rare occasions, without any accessories on. I suspect the roughness may be a dirty TBI injector. Everything else seems to be in working order.

I'm lost on the slow return to idle.

Any suggestions will be greatly appreciated.
Thanks,