bouncing vac gauge at idle ?

[clarkja]

Let's hear the main causes of a bouncing vac gauge.It is steady at idle in neutral(16.5 to 17 in.),but when in gear at idle the needle starts bouncing between 5 and 10 roughly.It bounces steadily up and down without ever evening out.I know that I'm giving a lot of info but just go over the common causes in general.

[gsmikie]

take a dollar bill and hold it with 2 fingers on one end then hold the bill across the tail pipe and see if it gets sucked into the pipe ...... (burnt valve)

[clarkja]

While in gear or in neutral?

[gsmikie]

neutral