my (i.s.x. 500,) developed a shaking symptom recently.
there is no cel or smoke from stacks.
kind of sounds like a Harley at idle at a stop light. kind of like a fowling sparkplug in small car.
it only does it seldomly when in neutral and idling, and also when the temperature's above 75 degrees fahrenheit. when the temperature changes to like 70 degrees or lower it stops and idles perfectly.

i changed the fuel filter, and even tried fueling up at different places just in case it might be bad fuel but still nothing.

it idles smoothly at 675 rpm. when the symptom starts it would spike up and down (675rpm to 650rpm).

anyone with any help would greatly be appreciated.

well I can say that on my truck with a 11.1 det it has a sensor that is connected to the go pedal & when it went bad it did something just like your describing. mine was actually under the go pedal. you had to take pedal off to get to it. it is some kind of speed sensor. this may or may not apply to your prob. but it's worth asking some one with better knowledge than I. my truck was a 95 intl. good luck.

hmmm. thanks heavyhaulers, i'll look into it.

I had also heard that there is a tube or two that have to do with EGR that need to be cleaned out occasionally. I was talking with a driver the other day that not cleaning these out will lead to what you are describing. The driver also said he just went ahead and bought a couple of extra stainless steel tubes and changes them out occasionally and soaks the removed ones in solvent to clean them for the next change out.

thanks. but according to peterbilt, my model year isx (2000) doesn't have a egr valve. so that rids of the problem. One of these days when it starts acting up again i'll take it in and have it checked out.

thanks for the input. i'll keep it posted...

My guess would be either an injector or injector harness gone bad.

It sounds like an injector problem. I know a guy who had a Cummins that would miss from time to time. He felt it was an injector, but it seemed that every time he checked it that he could not find the problem. He finally found it and fixed it.

at one time i had a bad injector wire. it would run same as a car that had a plug lose or off the spark plug.

I'll chime in here. Had same problem. Eventually it will be a problem at any RPM.

I will go with the majority here. Injector issue.

kimo