My heater blows cold air and my temperature rises to almost overheating. if you rev up motor temperature drops and heater blows warm air. What is problem.

You have to bleed the air out of the system, there is a small brass valve( maybe 2 valves in the front of the engine compartment ) that must be opened to allow the air to escape. Engine must be running while bleeding the coolant

If the vehicle is an manual gearbox, hold the clutch in until the engine has taken properly. If it is a manual rather start i neutral with the park brake on than in Park. Once the engine has started, let it idle for a minute or so before driving off slowly. Until the temperature gauge has at least reached the 1/4 mark, try keep engine revs below about 2500. All the while keep an eye on the temperature gauge, if it rises very sharply and the fan does not come on, there is a possibility that the radiator is frozen and the engine will boil and burst a hose. If the temperature does rise suddenly, stop and carefully feel if the radiator is still cold. If it is, shut off the engine and wait till the radiator has thawed. This will take a while but can be hastened by starting the engine for a few minutes to warm the engine compartment to help thaw the radiator. When water is circulating freely, you should see a sudden drop in temperature. Do not rev the engine too much, the incoming water will be ice cold and could crack something. This is not something that occurs often, especially if you try park the car where air cannot readily blow through the radiator overnight.

think it needs more coolant added when engine is cold

start with a thermostat...

A thermostat stuck in the open position can cause both of these problems

Check the heater coolant flow valve is fully turned on when heater selected.
Check the temperature regulation & heat/demist air flow vanes are operating correctly,
Check motor operating temperature is as per specification- if motor running too cold replace the coolant thermostat.

check coolant level ,must be low ,chck for coolant loss

Make sure your anti-freeze is full in the radiator.. If it is low, the heater is the first to go, but you wont see signs of overheating.. This I believe is also contributing to your idle fluctuation.

Let your engine warm up with the rad. cap off and see if the coolant level drops. and make sure your overflow is full. It blows cold air because there is no water getting to the heater core. And it shows a normal(ish) temp because the water needs to be touching the temp. sensor. I really do think there is air in the system and there is not enough coolant but hard to tell from here. Also as with overheating any time make sure to check your oil and look for any coolant as the head gasket seldomly holds together if the motor overheats.

there is a valve on the water pump and one on the thermostat housing open those up one at a time until you get a little bit of antifreeze come out then tighten them back up. All you will be doing is bleeding the air out of the cooling system. my car was doing the same thing after I changed my thermostat.