The air pump & EGR are not the same thing.

First, the EGR (Exhaust Gas Recirculation) sends exhaust gasses from your exhaust manifold back into your intake manifold in an effort to reduce emissions.

The air pump is also there to reduce emission. If I understand correctly, it force feeds air to your engine for a while after a cold start to reduce emissions. Someone correct me if I’m wrong.

I can’t speak for your car, but I did disconnect the EGR on my 95 GTi VR6 and my 97 Jetta TDi when I had them with no ill effects. I also installed a supercharger on the GTi and in the course of installation; the air pump had to be disconnected. The car ran really rich with a cold engine after that, I couldn’t say if it was because of the air pump being removed or the questionable engine management that came with the supercharger.

Why are you getting new manifolds?
You have a euro model, did you get headers?

I'd love to get some good *affordable* headers for my 420SEL. :D

Well yeah, I do have a euro car, but before 9/87, only certain models came with dual exhaust. I think the 500s and 560s only. So anyways, even though mine is a Euro 420, it has the US style 2-1 y-pipe exhaust and as you may know, the driver's side manifold flange wraps around the back of the motor and is parallel to the ground. Well I found a pair of used manifolds off of an 84 500SE euro that had duals so both flanges turn down. So now I can run dual exhaust. They are kinda rough (a little rusty and cruddy), but I am having them Jet Hot coated to make them all pretty :D

Air Pump & EGR
 

These are 2 different systems.
1) The Air Pump provides oxygen to the exhaust manifold for a more efficient burn of exhaust gasses. The airpump is a belt driven accessory (looks like an alternator, or A/C compressor) that pumps air through hoses and finally into holes in the exhaust manifold (as many holes as cylinders). If the pump shares a belt with any other acessories, then just simply measure for a new shorter belt if you remove it.

2) The EGR, Exhaust Gas Recirculation valve does just that, it re-routes exhaust gasses from the exhaust manifold to the intake manifold. I don't think that you'll see a huge performance difference by taking it off, but it sure does look better, and its one less vaccum operated mechanism to leak and give you a rough idle.

I of course do not endorse the removal of any emmisions related equipment required by law, unless the vehicle if for off road use only.

Re: Air Pump & EGR
 

Make sure that the AIR pump pulley doesn't also deflect the belt around something. There may not be a straight path from the fan pulley to the alternator pulley.

Sixto
91 300SE
87 300SDL
81 300SD