ALDA can fail in interesting ways, that can actually reverse its intended operation!

I've gone through a couple (broken seal on one, broken aneroid on the other). The aneroid one was a stumper - we couldn't understand why the car turned to into dog literally overnight between drive cycles. It seems an aneroid capsule in the ALDA had fatigue crack, vacuum lost, expanded the capsule, which pushed down on the limit plunger on top of the IP. Result equals dog.

The other broken seal failure, more common failure, means ALDA was holding pressure only intermittently, so the aneroids wouldn't compress, kept plunger down, dog. You get the idea.

ALDA is much better now that it is off the car and staying that way.

No ALDA means plunger stays up, nothing can possibly push it down, car goes as it should.

If you're worried about lack of overboost protection, refocus your worrying on something else, really. I've never heard of one case of these cars going into overboost needing to protect itself. You'd be lucky if all the overboost hoses, sensor, solenoid, etc. stayed clean enough to work when they might be really needed anyway.

If you're worried about black smoke, lighten up on the pedal. Ta-da!

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Cheers!
Scott McPhee

1987 300D