could be ur coolent gasket valve or what ever it's called....what year is it, when my valve got stuck open my car would rev up and down for a while till i replaced it....if it's a 94 then it located on the left side of ur engine...follow ur coolent hoses and you'll see a metal area where the rubber hose connects too...ur valve is in there...very easy to replace and inexpensive, if u need more detailed instructions email me a
jjanuszc@vtc.edu