I just like to ramble

The ARV in my SDL had a deformed plunger. It was leaking boost from the compressor outlet to the compressor inlet even with the vacuum hose disconnected. I haven't heard of anyone else having this problem.

And here's more rambling -

The ALDA puts pressure on a plunger atop the IP to generally reduce fuel. As boost builds, the ALDA piston retracts allowing the IP plunger to rise and allow more fuel. You might think of it as a secondary throttle. With the ALDA off the IP, you open the door to maximum fueling even without additional air charge. The IP introduces more fuel than the engine can burn and thus have smoke if you applying pressure on the pedal more quickly than the engine can build revs.

I don't know if you can do a visual test of the ALDA by applying pressure and watching the piston retract. Since you have to remove the ALDA to do such a test, it's simple enough to go for a drive with the ALDA off and assume the ALDA is stuck or has a leak if performance improves.

You can use the ALDA off a 617 if you need a replacement. Or bum one off the many folks who have eschewed the ALDA.

Sixto
87 300D