1991 skylark 2.5l rough idle, puffing exhaust

it was leaking from heater core. so i replaced it.

then it starts to idle rough and the exhaust pipe is like 'puff.. puff. puff. puff'

i tried to bleed air from the coolant system. and replaced thermostat. but air seems to be trapped in the hose that connects the radiator to the thermostat housing.

the way i tried for bleeding air is that i installed the spill-free funnel to the coolant reservoir tank and let the car idle for about 10 mins.

i didnt see the fan running. the car lacks temperature gage which makes me scared to let it run more than 10 mins.

but the heat comes out well from the vents.

please help me

Sure you don't have a misfire?