It isn't under the car... It's along the bottom of the turbo assembly.

Basically the wastegate is the item that allows pressure to blow off and keeps the turbo from going to PSI levels that will destroy it and your engine... a kind of turbo governor as it were. As such, if the rod has fallen off or seems to have become slightly unscrewed, etc., you MAY want to have a pro handle it... its possible to set it for like 13psi or thereabouts, which is not what you want. Of course if the clip just fell off it shoul dstill be set properly, and all you need to do is reconnect it. There is also an emergency kill switch on the system above the gas pedal in the cabin, but that shuts off fuel completely.

When pressure increases past a certain level (usually like 7psi or something) the wastegate connected to the turbo hoses via a small vacuum hose gets pushed open. The level at which it can open is set by how much you screw the rod in (the rod is spring loaded and actually keeps the valve cover closed).

There is a clip that keeps the rod in place. If that clip rots or falls off the rod can come undone. In such a situation there wouldbe no counter pressure to keep the wastegate door closed, and it would be able to flap open at the slightest pressure... I think it just kind of drifts around when the rod falls off.

You can't see it from the top, and you can't get underneath to see it without a lift, jack stands, or ramps. However, you can put your hands around the turbo and feel for it... if you feel a single rod about the diameter of teh middle of an antenna mast running parallel to the turbo its fine, if you feel something hanging perpendicular and loose it probably isn't.

good luck,
rt