1987 Oldsmobile Delta 88 87 Oldsmobile

What makes an idol go up and down changed spark plugs changed mass air flow sic. Changed a sincer nxt to the mass air. It dies sometimes when I come to a complete stop. It has died when once why I was driving it. When im driving at a steady speed it kinda jerks like its trying to die out or its flooding or something I hope this can help me really need to get it fixed