Idle problem-need help!

91 probe-when the car is in park it idles at 1500-2100. when you put it in gear its normal-less than 1000. What do you think the problem is & what can I do to fix it? A machanic used the Idle control to fix it but nothing happened. Also, the stearing wheel shakes when stoped at a traffic light, why is this?

Thanx for any help!

lol i have the same problem, im gona go clean my throttle body tommorow, its probably carbon build up on the throttle plate, its sucks, if not im guessing its sensor related, i got a check engin light that comes off after i get abover 2300 rmps, i dont no i lazy tho, and my car is screwed my pistons rings are going so i might leave it, kina lost intrest in the damm things...
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Is it an automatic? If so it could be a tranny sensor

it turned out to be a oil build up on the throttle plate, my turbo seals are gona causeing oil to leak into the motor, so it sucks,

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