Since the last time i put my motor back in i've had a low vacuum. It's constant around 10. I checked and replaced the throttle body gasket and also the intake manifold gasket. The vacuum reads constant but the rpm's will flucuate a little bit. What else could be causing it to run like this. I already checked all my vacuum lines as well. The timing isn't the problem either. What else could it be? 02 sensor possibly?

 

If your only pulling 10" of vaccum, perhaps your exhaust, namely your catalytic converter, is clogged up.

Your valve lash could also be set too tight.

Do you have a cam with a lot of overlap? That'll drop manifold vaccum as well.

If your gaskets were the culprit, you would have a hunting idle, more than likely. And your O2 is certainly not at fault either.

What kind of mods/maintenance have you done to it lately? This problem pop up from no where?