OK my girl just got this 94 celica St 1.8 7a-fe when the motor is cold the car idles and runs fine but when it warms up the rpm jump around from 800 down to 600 rpm. But only dose it when its in gear but when its in park or neutral its fine a lil ruff but fine and some time when I am pulling a hill and I step on the gas it cut back a lil. Plz help driving me crazy.

Do a regular tune-up:

Spark plugs
Spark wires
Cap & Rotor
Fuel Filter (if you trust yourself)
and clean the throttle body
also run some fuel system cleaner

God what the previous owner has done or hasn't

The previous owner bet the car to hell.
OK ty I did the spark plugs already ill try the others to.
Someone told me the sic valve could be dirty or bad? And is do where is it

My iac valve is bad need a new one anyone got a spare one?

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get some intake cleaner and spray the iac first, if that doesnt work then proceed to buy a new one