1991 Accord runing bad

Hello my car is A 1991 Accord with almost 200K miles. the problem is when the
car is cold it runs pretty good but wans it get to normal heat it start to
miss fire and the RPM start to jump UP and Down but ingen sound the same for
example if I going 45MPH the RPM should stay about 2000RPM Not jomping too
4000RPM or 3000RPM

When I going 45MPH and the car is at normal heat the car what to stol whayl
runing
when you step on the acelader when shifting or what to go faster that when
it start miss fireing or
what ever it is

 

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Sounds liek air in the cooling system. When thermostat opens the coolant
drops below the sensor and the computer thinks the engine isn't warmed
up. Mixture and timing changes and engine runs badly. Fill rad and
reservoir to the MAX mark and do it again next day too.
'Curly'