am not sure sa throttle kaka tappet lang sa isuzu.pero dati ko na na notice yung gaspang ng andar.na check ko yung muffler need to be replace,dami na butas.but i think hindi lang yung muff ang contibutor ng magaspang na andar,di ko pa na check yung mismong exhaust manifold.
Maski bago feed pump or even fuel filter kung hindi air tight ang hoses/clamps bale wala.I have seen this mistake too often. One way to confirm this is to twist the clamp/hose from the steel tube.