I started my car up this morning and heard a little bit of knocking, I pulled it into the garage and after putting it in park the idle started going from 500-1500 rpm and it would slowly get lower and lower then died. I gave it about 45 minutes then started it again, no knocking. So I pulled out into the driveway and put it into park then the idle started jumping again. I gave it a little gas and it seemed to quit after running for a minute and being revved a little. Weird.. Any ideas?