Don't, it's bench set at the M-B factory (and marked with a paint seal)
to a balance between power and minimal smoke on acceleration.
The ALDA contains two sealed metal bellows that slightly expand and
contract as the turbo's boost pressure is applied; this minute
contraction is applied, via some internal levers, to the fuel rack to
add fuel to the engine for power during acceleration. The metal bellows
can be broken during someone's "adjustment" and they're NOT available
from the dealer, only from Bosch so keep that in mind before doing
anything there. The ALDA is part of a small subsystem that requires a
bit of maintenance which ought to be done before anything else.
Instead of messing up the ALDA, clean out the banjo fitting; it's at the
aft end of the engine's intake manifold and gets clogged with carbon and
oil. A 12 mm wrench is needed and a, 2" piece of wire or paper clip.
Remove the bolt, which is hollow and attaches the banjo fitting to the
intake manifold. Clean both the hollow bolt and the banjo fitting. You
can test drive the car without these in place to see the engine's flat
performance without this subsystem (don't leave the hollow bolt lying on
the engine). You'll hear the turbo's boost pressure hissing from the
engine (harmlessly) on acceleration when the rpms exceed 2,500.
If, during the test drive, you notice NO performance difference then
there's more work to be done. Reassemble the banjo and bolt and trace
the plastic line over to the switchover valve (left firewall) to ensure
its rubber connections are good and not cracked or leaking and then
follow the line to the ALDA, again checking for leaks. The switchover
valve is a safety valve to prevent a run-away engine condition - it can
be bypassed (jumped) to test the valve. The bypass valve may be dirty or
stuck open which, like dirt in the banjo, prevents the turbo's boost
pressure from reaching the ALDA.
If the engine is still flat after this work AND a check is made to
ensure the throttle linkage opens the injection pump's throttle lever to
its full throttle stop (between the IP and engine) then it's time to
look at the ALDA - as a last resort. First, is the paint seal or
aluminum cap on its adjustment screw (center of the circle) intact? If
so LEAVE the ALDA alone. If not, someone's already been there and may
have broken the bellows. If someone has messed with the ALDA and you
want to as well then turn the adjustment screw OUT 1/4 turn only. Test
drive the car and watch for exhaust smoke vs. acceleration. Too much
acceleration smoke indicates too much enrichment adjustment so back off
by turning the adjustment IN. Keep a note of each adjustment so you can
get back to the starting place.