Civic EG

Hello civic eg

i have a wee problem that hopefully someone here can help me with

Firstly I am Driving a D15B3 carb and its currently summer in Cape town

while driving and braking then gearing down from 4th then 3rd then 2nd my car just chokes off and i start
i have checked then vacuum pipe on the carb which is on properly and replaced the HT leads and checked the Battery.
the car has got a mis on idle so im thinking could it be the Idle valve on the carb?

if im driving and i double clutch down gear to keep the revs up shes fine
also if i gear down then put into neautral and brake left foot while keeping my foot on the gas shes fine

please help

thanks guys