Previa 1994 keeps overheating have replaced anti freeze but the temperature still going up ,done valve test still the same it drives and maintains right temp but when idle ie waiting in traffic the temperature soars back up

replacing the radiator with a new unit is one fix and if the water is coming out at the thermostat housing area area replace the housing as it probably is badly corroded inside
it is essential in cars with aluminium heads and other components that the anti boil anti freeze be maintained at that ration of 50/50
that stops corrosion as well as stabilizers the coolant temperature parameters

- Check the radiator cap for proper sealing.
- Blow air from outside and inside of the radiator to clean the fine dust accumulated in the feathers and fins.
- Check the radiator for clogged inside. Clean the radiator after disassembling it.
- Check the water pump belt for looseness or wear.
- Check the thermostat valve.
- Check the cylinder head gasket or re-torque the cylinder head bolts.

If the car uses anti-freeze without leaking, it is going out the tailpipe. You either have a bad head gasket or a crack in the head or block.

All cars do!

The overheating is caused by the sludge. It is very easy to correct this problem. Remove the radiator cap and open the drain valve at the bottom of radiator. If possible, remove the reservoir and flush out with water. Make sure to get all sludge out of reservoir, then reinstall. Once the radiator stops draining, insert water hose (without nozzle) and turn water on. Keep the drain valve open. Run water through radiator until it runs clear. Once it runs clear, start the engine and let it run while keeping the water running through radiator. Allow engine to run until the thermostat opens up. Continue running water through radiator with engine running until the water from drain runs clear. Once you have done that, turn off the engine. Close the drain valve and refill radiator with proper mixture of coolant and water. Once radiator is filled, start engine and let circulate through engine. Coolant level will drop as the coolant starts circulating. Shut off engine and top off radiator. Fill the reservoir with the required amount of coolant. Testing the coolant at least once a year will help prevent this from happening again. Coolant should be replace a minimum of five years, less if coolant bottle specifies.

Blue smoke in the exhaust usually means oil is leaking into the compression cylinder and is burning with the air/fuel mixture. This would definitely cause hard starting.
As for how it's getting in there, that depends on how the car has been maintained. How many miles are on it.
First thing you should do is check your oil level. Make sure it's full. Keep track of your oil consumption for at least a week. Knowing how much you are using up can give you an indication how it's getting in there.

This could mean worn rings and cylinder walls or bad valve seals. It could also mean a crack in the block. This might shed some light on the cold air problem as well. Especially if your car overheated recently. Regardless what the cause is this is not a week end job. If your not comfortable with the thought of engine parts laying around find a good mechanic.
I really hope this helps and good luck.

YOU COULD HAVE A BLOWN HEAD GASKET, MOST REPAIR SHOPS CAN DO A BLOCK TEST WHICH WILL TELL YOU IF HEAD GASKET IS BAD, ALSO CHECK TAIL PIPE FOR WHITE COLOR SMOKE.

make sure thermostant is good. most important is to make sure you didnt blow a gasket when it overheated, if you have a 3.8 engine those are famous for blowing headgasket. anyway have a block test done first, its a liquid they use to see if exhaust gases are entering the cooling system, good luck ,hope this helps.

when you replaced all of that stuff on the vehicle did you make sure that you don't have a vapor lock in the highest anti-freeze line? to fix run vehicle with line disconnected so air can escape then reconnect. if that dont work you will need to put a T splice in the top anti-freeze line so when the vehicle is running you can open the valve and let air out.

First you need to make sure the fans are coming on and if they are make sure they are coming on when the car is over heating because there is a fan relay by your fuses if its going bad it wont turn the fans on or it willl only turn them on sometimes..