.accelaration prob

1993 mazda b2300 p/u with a 4 cyl the engine starts up idles fine but when you put it in first gear and step-on the peddle it wont accelarate properly like when the peddle is stomped to the ground it just bogs down and does'nt pic up speed what could it be ?,, ( tps, idle valve,maf?) this might help< when the engine is in neutral and i manually apply the throttle at the throttle body (hold open) then the engine rpm go up and down, up and down with the throttle held in one posistion say 3/4 open..4 cyl engine with plugs on both sides, two coils