My 4runner started over heating on me a few weeks ago.. it would only over heat when at idle. (checked the fan cluch it was good) it has not over heated on me in a while but i also have not been sitting for a long period of time... i was sitting at a stop light and i noticed that the heater was blowing cold, i started to drive within seconds the heater was hot... but when i stoped at another light took about 20 sec and if was blowing cold again...??? any thoughts

 

First thought is thermostat, I would go OEM for this item although expensive.

 

Yes, start with Thermostat AND a "heavy-duty" cooling system flush.
try toyotapartsdeal.com for OEM at great prices.

Flush like it says here on the bottle of Prestone Cooling System, Flush solution:



Make sure you also back-flush the whole system.

 

Have you checked the fluid level in the rad and overflow bottle?

 

^^ I would start here, the basics. The engine can't stay cool with low coolant.

What is the condition of the coolant? Nice and clean? Full of rusty gunk?

 

^2 for checking coolant level, saying your heater blows cold and then hot once you're moving is a flag-waving indicator of low coolant. Does your rig have rear heat? The lines that run from the front to the back are prone to corrosion and leaking without showing signs up front.

Next, what is the mileage on your timing belt and water pump? They really should be replaced every 100k miles or so. The water pump is hidden behind some covers and it is difficult to determine if it is leaking.