rough idle with oil cap off

[ltbuick]

I just replaced plastic upper intake manifold. I tore all the way down to lower intake. I replaced everything including water pump. I was wanting to know if it is normal to hear a high vacuum sound when vehicle is running also when I took oil extension off to put the engine shield on it wanted to start to miss.

[ltbuick]

I just replaced plastic upper intake manifold. I tore all the way down to lower intake. I replaced everything including water pump. I was wanting to know if it is normal to hear a high vacuum sound when vehicle is running also when I took oil extension off to put the engine shield on it wanted to start to miss. I checked all vac lines and replaced loose ones. When car is idling it idles at set rpm, no driveability problems. Idle does not bobble engine sits like perfectly tuned. JUST STUMPED. Thanks

[richtazz]

check your PCV valve, as they can get clogged when the upper intake fails. A clogged PCV will cause high pressure in the crankcase.