IP issues - won't throttle up until 80 percent open -possible hole in ALDA diaphragm?

[Goldenvoice]

Time to start discussion on an issue that's plagued our 82 300TD since we acquired her 4 years ago.

The engine does not throttle up until the linkage is around 80 percent+ of the way open. If, with the car idling in neutral, I throttle her up, I can watch the plate on the IP - she barely comes off idle through most of the linkage travel, then finally throttles up once the IP plate is around 3/16" from the full throttle stop.

Driving her is with my foot to the floor - much of the time. When I questioned our mechanic about it (before he retired), he said "hole in the ALDA diaphragm".

Now, I'm wondering if that was a 'shot in the dark' guess on his part, or pure experience. Can I test this with my mighty-vac? Anybody else have the same problem? And what solved it?

Needless to say, the transmission doesn't shift well on it's own either - it's a delicate "with your foot" thing...