2002 Chrysler Neon

Engine Mechanical problem
2002 Chrysler Neon 4 cyl Front Wheel Drive Automatic 65000 miles

Make car rev's up and down in rpms. Sometimes it accelerates on its own. When I am driving and pushing the gas it runs fine, but as soon as I release the gas it shakes voilently. I have replaced the spark plugs, and air filter. I also just replaced a fuel injector 2 weeks ago. Can anyone tell me what is wrong with my car?
March 24, 2010.

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