A few weeks ago, I removed the intake to complete the polishing. Believing it was a good idea, I replaced many of the hoses with silicone. Since then, I've experienced a higher and sometimes erratic idle. For instance, when slowing to a stop with the clutch depressed, I can watch the tach bounce a few times until I stop. I was extremely thorough with the lines, but there is a possibility one could have a pinhole. Has anyone needed replace the gasket between the intake and block??

 

When you are replacing the silicone hoses I know that there are alot of silicone hoses, well check to see if you hear any hoses making strange noise maybe it is not securely in place or it may not be the silicone hoses you are changing but it could be old vacuum hoses are worn out. And also check to see if the intake plenum is probably install. Maybe it could be the gasket between the blocks.

 

Are you getting the correct boost pattern? If there is a bad gasket, there will be boost leak and you won't get full boost.
After you polished the intake manifold, was it cleaned properly (outside and in)?
Check and make sure the throttle cable is re-installed properly.