Start with the basics. Clean out the lines and fittings going to the ALDA. They have a tendency to clog with soot. There's also a switchover valve on the firewall in the ALDA line that can clog or fail. Check that it is clear.

One of the often suggested tests for air is to install a clear piece of vinyl tubing in the return line to the fuel tank. If the fuel system is working properly and you have no leaks, it will be a solid column of fuel. If you get foam or bubbles, you have air ingress somewhere.

Check for excessive axial or radial play in the turbo. If the turbo is worn out, all bets are off as to how well it works.

I see you're in California. You neglected to mention which year model you're dealing with. Does this car have the trap oxidizer?

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]