So I just installed a fresh 4.6 long-block in my '98 4x4 xlt and I have a noise coming from the manifold area. Thought it was possibly valves or timing chain. Took it to dealer and they diagnosed it as the Intake Manifold Runner Control. Never heard of it!!! Problem is, I can't find that part for this motor. Is it inside the intake? Do I have to replace the whole intake? Dealer didn't tell me, once I said I would do the work myself.

 

If the motor has it, it hangs under the intake in the block valley.
If you can look down behind the alternator, under the intake, you may see the electrical connector on it's front.
That runs the motor to open/ change the air path.
This large Plenum is insulated for heat rejection.
If it got cracked some how, it will leak outside air, in.
Good luck.

 

Thx Bluegrass. Found it. Ordered new lower intake manifold on Partsgeek. $178.

 

Looks to be about a 2-3 hour job.