low and high idle on 1998 GMC Jimmy

Last week i went to start my 98 Jimmy and when it turned over it idled really low then idle really high then low and then high then it usually cuts out and dies also smell gas while itd doing this... have any idea where to start as far as what could be wrong

Asked by for the 1998 GMC Jimmy
Usually having the throttle body cleaned by a repair shop will solve this and you can find one here