Throttles up at certain times and won't come down

I am 100% disabled veteran on a fixed income. My 96 anniversary. Lincoln throttles up at certain times and won't come down. Usually around 2000. I took to mechanic and they can't figure it out because it didn't do it for them after 2 wks. I picked up the car. Ran gr8 and then when I started it back up, after engine was hot. It reved up again. Called the mechanic so he could hear it. He wants to replace the entire throttle system, over 1000 dollars. But I've been researching online and this seems to be a sensor problem. Would you recommend I just change the throttle sensor to start, and perhaps it will fix it? Please, I have to be able to get to my dr's and right now I don't feel safe driving it. It has about 114000 miles and rides just gr8.

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