sometimes my car's rpm meter drops to 100-200 rpm and the whole engine shakes. i forgot what it means can someone help me out?

 

Check to make sure that you have a fuse in the 3rd slot down from the top right of your fuse box (fuse #25), and that it is good. If it is missing, or blown, your ECU will be reset every time the car is turned off, which makes the idle really rough. Another way to check is to leave the car turned off, with the door open, turning the head lights on should make the warning chime sound.

If this is not the case, I would suspect a problem with you EACV (Electronic Air Control Valve), which controls idle speed.