I have a ’92 Toyota Pickup with 200,000 miles on it. Today when I started it up (the engine was cold) it began idling around 3000 rpms which is faster than normal. I drove it 1 mile, got gas then drove another 2 blocks before it finally died down. At that point I noticed that the engine temperature was just below the red area (hot)….but the heater/defroster was still blowing cold air. The engine temp didn’t cool off for another ½ mile or so and that’s when the heater finally started blowing warm air. What could be the cause of this sudden “erratic” behavior and how can I fix it?[

You might have a bad coolant temp sensor which is why the vehicle is idling so high.

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Originally Posted by this8384

You might have a bad coolant temp sensor which is why the vehicle is idling so high.

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Would that cause it to overheat then when the idle settles down it cools off to normal?

I'm not 100% positive on that; I would have a computer diagnostic done to determine what exactly the problem is. You might even have a vacuum leak which is causing the high idle. A bad thermostat could also be causing the overheating.