I have a 318/5 speed 97 Ram with 150k on it. I replaced the intake manifold and plenum gasket at about 110,000 because I was using and saw oil down through the throttle body. Everything is OK until now. I'm using oil again like crazy and it is pinging under load. This time I do not see oil down through the throttle body. I am also getting a surge at idle EXCEPT when the AC compressor is engaged. For some reason the idle smooths out when I hear the clutch engage.

I decided to follow the steps in the TSB to detect a leaky manifold gasket:
1. disconnect breather hose from manifold and attach Vaccuum guage to hose. -done
2. disconnect pcv hose from manifold and pcv. Cap pcv and manifold. -done
3. start engine. do not let crankcase build pressure to more than 3 psi. -done

I have 15" of vaccuum! When I give it some gas it drops to 7-8".

Is this supposed to be 0" of vaccuum? I just want to make sure that the gasket is bad again before I throw money at it.

I just had to change mine again this summer, only this time I installed the Hughes aluminum plate. If you plug the PCV side on the manifold and start the engine, the breather side hose from the valve cover should not have a vacuum on it. While running, you should hold you finger over the hose and it should build up a little pressure, if it is pulling, then your gasket is shot.

Unreal, I can't believe a small leak in the plenum will allow the crankcase to pull 15".

Just making sure I was toubleshooting correctly. Thanks.

It's the lower intake gasket on the bottom of the intake. Remove the intake, flip it over, remove the plate on the bottom, reinstall the intake. I have no idea why they ever even put this on there.