I never had this problem until the belts were replaced. It started as that once it was warm it would idle fine until I drove for an hour plus without coming to idle, then when I get off the free way it will barely idle at 500 rpm. Now it once its warm it will barely idle at 500 rpm and I just cant seem to adjust it higher. It runs fine when on the throttle and it is also backfiring alot when I let off the throttle while in gear. Can some one help me pinpoint my issue.