how to tell if a cam is going bad?

[shmed]

like the title says how can I tell the car  was running great all week then out of no where  it starts idling rough an the boost vac gauge swings up an down like usually its steady 15 inches  vacuum   now at idle it bounces   15 7  19  4  all over the place.
any help appreciated
thanks dave

[shmed]

did a little digging an found a crack on the header,  an the turbo is  shooting oil thru the motor. 
question I read the pushrods are supposed to spin is this when its running  or will they spin while  cranking with the key?
(flat tappet cam)

[earlbrown]

they won't spin while running the starter.     

With the vacuum gauge, the swings are defined many ways.  different manors of swinging and/or twitching for different symptoms.

[daveismissing]

With the vacuum gauge, the swings are defined many ways.  different manors of swinging and/or twitching for different symptoms.

http://www.ihadav8.com/forum/index.php?topic=3238.msg49621#msg49621