http://www.dieselgiant.com/mercedesaldaboostsystemservi.htm

Follow the hard plastic opaque colored line that goes from it to the the device on the firewall, behind the brake booster. This device is the Overboost Protection Relay (OPR). This device (and lines), if clogged will prevent proper boost from reaching the ALDA, which means your engine will not receive the proper amount of fuel relative to how much you are pushing the go pedal.

The OPR needs to be taken off, cleaned with carb cleaner and in my case, wire to reem out the soot. There is another hard plastic opaque colored line that goes from the OPR to the back of the intake manifold. Both of these lines need to be free from soot. Also, make sure the banjo bolt at the back of the intake manifold is free from soot as well.

Remove, clean, install and watch your frown turn upside down with "new power" from your diesel.

The difference was night and day.