1989 Isuzu Trooper 89' Trooper

I Have an 89' trooper that starts up and runs just fine in high idle at cold start however after a minute or two it will slowly give its self less and less gas and stall. If I give if I hold down the throttle it will stay running. I tried adjusting throttle and idler, it just starts in a really high idle and then stalls out. Need advice on how to trouble shoot this problem.