Remembering why I
dislike working on
AO Silver Member
Join Date: Sep 2001
There is a bias in the TB that holds it slighly open when no drive is applied - this is the limp-home thing that gives enough air for a fast idle. Normally, I'd expect that the TB would be tighter shut than this, so it will always receive a certain amount of drive to close it down, hence the whine. It is possible though, that later versions have a different strategy and after doing an initial position check, and just 'relax' until actually needed. Also possible is that it was a different temperature when you compared the two engines - the TB is used as the IACV on these, so again, depending on how it does it, the TB may be set at an appropriate starting point to fire up the engine (the old 12V motronic system held the IACV at about 50% open with ignition on but engine not running). All these notions about the actual strategy are supposition though - I don't know, and haven't looked at the late 24V motors - I just jump in the 166 and drive it!
If you are concerned, it might be worth your while having a look-see to make sure it's clean inside the TB bore and there isn't anything preventing free movement. If it's clean in there, don't fret about it. The throttle plate should move freely enough by hand - be gentle with it, you'll feel a fairly strong spring pressure but it should move smoothly enough (with igniton OFF!).