Engine idle toohigh after warms up - 1994 Toyota Previa

Are you having an idle issue ??
Vehicle equipped w/Tachometer ??
Cold engine idle speed ??
Warm engine idle speed ??
Warm engine idle speed @ A/C requested on ??

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Possibly an idle air motor for your idle problem or a vacuum hose off.

You need to have the choke adjusted so it runs on a fast idle so the engine can warm up or you may need the carb to be rebuild and adjusted properly.

That would be your engine "choke" functioning. It's not a problem. The choke engages when engine is cold and shoots extra fuel to the cylinders to idle the engine up especially in cold with. Once the engine has sufficiently warmed up, the engine will idle back down.

COULD BE THE IAC VALVE "IDLE AIR CONTROL".
LOCATED ON THE THROTLE BODY, TRY REMOVING AIR INTAKE HOSE AND WITH INTAKE CLEANER SPRAY OPENING AND ALL HOLES IN OPENING WITH CLEANER.VALVE IS STICKING AND RAISING IDLE. CAN'T HURT AND YOU GET A CLEAN THROTLE BODY SERVICE.

it seems that the auto choke setting is maybe wrong or there is a problem with engine management, or a worn part which is sticking.

when cold, the engine should be higher as the choke will be on but a warm up idle of 1200 seem a bit high i would expect around 800 and then on restart if the engine is warm then the choke should be off but the idle being too low indicates one of the above.

has it got a idle control valve, have tried adusting throttle cable slightly

THE COOLANT LEVEL IS LOW

on the older hondas even the newer ones idle speed is coolant temp controlled.

when the engine idles up the electronic coolant temp sensor is submerged in coolant and reads warm, so the engine computer idles the car down. the coolant level if low than drops from around the coolant temp sensor and it says the engine is cold, so the engine computer idles the car up.

which results in the constant rise and fall in engine rpm.

ADD COOLANT TO THE RADIATOR AND WATCH THE CAR MAGICALLY FIX ITSELF.

you might wanna use a thinner lighter oil

The high idle is caused by the choke and the high idle on the carb. It is working normal and you do won't to warm up this motor before going. When it is warm and you hit the gas it activates the choke pull off to bring the idle to normal. Your mechanic is used to fuel injection that will control the fuel/air mix according to temp. I still let my injected cars warm up so the oil can thin a little. If you jump on the highway with cold thick oil it can all wind up in the to of the motor.