when i start my car up it idles at 1900 rpm, after driving it goes down to 900, then if i turn it off and then back on it will idle at 1900, why would this be? also, after i drive for a while it will idle at almost 700 rpm, any advice? thanks in advance

 

when its cold it idles higher to warm up the engine faster so its okay to drive. when its warm, it doesn't need to heat up so it idles as low as possible. just remember never to beat on a car that isn't warmed up