New quiet lifters
Join Date: Feb 2012
Location: United Kingdom
County: Greater London
Shadowarcher, from what your mechanic has said, you have a metal inlet manifold with an external linkage to the swirl flaps. That type is relatively benign, the pivots leak (which loses air and causes rich running = black exhaust smoke), and the actuator rod pops off the tops of the flap pivots, so they don't work as intended.
You can get repair kits to fix the leaky pivot issues and the bar detaching (ebay). Or you can remove them entirely (which is best done in conjunction with deleting the EGR valve). Removal does mean the inlet manifold has to come off and the pivot holes sealed, usually by welding.
As a temporary fix the flaps can be locked in position and the pivots sealed, using silicone sealant or similar. But they must be locked open, not closed as your mechanic suggested. When they are closed, half the inlet ports are blocked, which is fine at tickover and low revs and causes 'swirl' turbulence for better combustion, but at >1,500rpm or so will prevent the engine breathing properly and have a dire effect on power.
In fact it's a reasonable guess that is what has happened. The actuator bar has fallen off and the flaps have rotated into a closed position, so the engine is now working with 4 small inlet ports instead of 8 and has an much power as a lawnmower. Plus, you're probably losing boost through worn pivots.
Long term, it's best to remove the manifold, remove the flaps, clean the interior of the manifold which will be full of carbon/oil gum, delete the EGR and have it mapped out. But as a quick bodge, sealant or hot melt glue will be fine and it won't cause any damage to run like that indefinitely.
You will have to keep the actuator motor connected regardless, else you'll get an MCSF and fault code unless you have the flaps mapped out, which is usually done at the same time as mapping out a deleted EGR.
The other later type, metal flaps in a black plastic manifold on CF4 16v engines from ~2006, fail too, but they fall off and cause bad engine damage. The linkage is not visible, as it's built into the underside of the manifold. It doesn't fall off, but the whole thing is a hand grenade, and inevitable. They need to be deleted ASAP before they delete some valves/pistons.