1997 Daihatsu Charade CS G203 1.5i man...

Hi,
I have a 1997 Daihatsu Charade CS G203 1.5i manual that stalls when the car has warmed up.
The revs seem to drop too low and the car stalls.
This always happens when you clutch too slowly (take too long changing gear) while accelerating or when coming to a stop and you take it out of gear and roll to the stop. You have to usually keep your foot on the throttle a little to prevent it from stalling.
Every mechanic (including the manufacturer) cannot fix it - their only remedy is to increase the idle and the car ends up idling too high all the time.
Does anyone have a solution?
Cheers.