My 1998 mazda b2500 will barely idle and has no acceleration. The idle will occasionally smooth out. I have changed the fuel pump, fuel filter, idle air control valve and the throttle position sensor all w/o success. The plugs and wires have about 18k on them. This all started one morning last week when I started the truck. Prior to that it was running fine. No check engine lights are on.I would appreciate any ideas on my next step.