A missing rubber grommet for the vacuum tube that sucks off the PCV valve and the MAP sensor caused a major vacuum leak that in turn caused my transmission to slip, lifter clatter, a very rough idle, engine to die while stopped in gear and a CEL.

So, if you're experiencing any of these problems, you may want to have a look at that grommet. It is on top of the intake manifold, just in front of the throttle body. The grommet is a dealer item and only comes with the whole tube assembly. The good news is that it's only $11.

I also discovered that the grommet for the vacuum tube to the rear valve cover was nearly destroyed. That tube assembly was $28 so I sourced a grommet from Autozone for $3.

 

I am with you on this. This has been an issue with auto's for along time.
information you have included is great. Thanks !

 

My experience with 3100/3400 is that the grommet on the back valve cover disfigures often, but despite having a "loose fit" never usually causes too many problems (it just vents to the atmosphere a little and does not return as much to the air intake).

But the rest of those connections, absolutely, they must be in good shape, properly sealed.

Good share and good to hear that entire rig is not expensive at all!