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1992 Mazda mx-3 automatic idle problem

Ok, let me start with I know nothing about cars. I am sorry if my question is vague and stupid.

My girlfreind bought a car, and her sister told the guy it was idling too high, so he adjusted it. When I went to pick up the car to drive it home (She does not have her licsence yet) I started it and it died right away. So i started it again and gave it some gas (if I did not give it gas it idled at about 100rpm and would die. Basically If i was not on the gas it would idle really low and die. So I adjusted the idle to be higher. Now it idles at about 500rpm in Drive, but about 1400rpm in park. I should put it to idle at about 800rpm in Drive right? But that would throw the parks rpm to probably 2000? Why is there such a difference? Is that really bad for the car to idle that high?

Next time I see the car I will check the transmission fluid. Could that be a possibility?

On fuel injected cars the idle is controlled by the computer via the Idle Air Control (IAC) valve, and you cannot adjust it by turning a screw. What you did was open the throttle, which is why it idles so high.

Whoever adjusted it the first time should not have done what he did, either. Turn the screw back to where it was, and have someone check the operation of the IAC valve.

Ok thank you. The only thing is before he messed with it it was running fine. It was not idling to high or anything, its just that her sister said it was so he changed whatever he changed. I am not trying to ignore what you said, should i still get the IAC valve checked out?

Thank you again

Well, if you can undo whatever the first person adjusted everything should be fine. If the car idles smoothly and at the correct speed there’s no need to mess with the IAC valve.