Hello everyone,

I'm a newbie here so please forgive me if I am asking this question in wrong place. I have 91 accord and when I start it (anytime it's cold), it's rpm goes up and down from 1500-2200 and after 8-10 minutes running idle, it settles at 800 and the heater is blowing hot air too. But once I drive it for 4-minutes, the air becomes cold and the rpm starts to go back up again.

Could someone please suggest how I can fix this problem?

Please let me know if you need any more information about my car. It's 91 accord, 4 cyl and got about 420K on it.

Thanks in advance for your help.

 

EDIT: When the engine is cold, remove the radiator cap and check that the coolant is filled to the top. Also check the level in the clear plastic overflow bottle.

Does the coolant temperature gauge lower when you lose heat in the car? If yes, then you need a new thermostat.

Get the thermostat from the dealership. It is also a good time to replace the coolant. Remember to bleed air from the coolant.