I have a 1999 7.3 diesel. I start it up when its cold to warm up. It goes on high idle , like it is supposed to, but the exhaust will hiss on and off not smooth and even . It also does it driving down the road it makes the truck jerk or lunge. If it is over 40 or 45 degrees it won't do it . Other than that it is a true work horse and will never own any thing else.