I have bought a 87 f-250 4x4 6.9 auto trans. and most every time after i crank it up it idles fine for about 3 to 4 sec. and then starts to miss and idles bad, iradicly. I have to rev it up a couple times to get to idle normal, then it runs fine no problems. It does it both hot and cold. Is the injector pump going bad?