hook avacuum gauge to port vacuum should stay steady if it shakes valve train problem.
Do a compression test. When you find the cylinder that has low compression, shoot some oil into the cylinder and take another reading. If the reading changes very little it is probably a bad valve. If the second reading is much more than the first it is probably worn rings.
You can tell a bad valve by doing a compression test.
You can tell when a manifold tuning valve is bad when oil is leaking through it. You also can tell by inserting the dipstick into the valve and seeing if oil comes out through the dipstick.
Diagnostics
No, some rattle is normal.
Bad bearing Bad valve
Start the engine, and spray a little carb cleaner around and on the EGR valve. If the engine changes sound are idles up are down then the valve is bad.
if you get to get gas the car has hard time to start
I have read that a bad PCV Valve will contribute to gunking up your Throttle Body, which could lead to irregular acceleration issues. I am certain that there is more to a bad PCV Valve than that, as this is an Emission Control item, but hopefully someone who knows more will chime in. SUBMITTED: Friday, 03JUN11
bad valve seals, bad piston rings bad valve seals, bad piston rings
If your car has one, take the vacuum line to the modulator off and if there is fluid inside, the modulator is bad.
Check the compression of the cylinders you will have a low reading in the one with a bad valve
Which kind? Exhaust or intake, run a compression test. A burned valve will show up as low compression on one cylinder. A blown head gasket will often show up as low compression on TWO cylinders. If you suspect a bad PCV valve, jsut replace it as part of the tune-up.