Vacume questions and issues.

[VanguardSR3]

Hi all so recently bought a 2002 1.9 tdi sport estate.

car has been good for me so far, a couple of things that have peaked my interest and confused me a little.
this is my first diesel car and as I've come from a 210hp polo 20vT I don't know what one of these would normally feel like so i may be missing it feeling under powered.

issues

1.) The car when coming to a stop occasionally, will act as if its about to stall for a split second then recover itself.

2.) car has allot of vibration at like 2k rpm when driving, car averages 37 - 47mpg.

3.) i have found that the nipple from the vacuum pump at the back of the engine has quite a bit of play.

4.) when plugging in my obd tool to look at the vacuum pressure, the car displays -30Hg even at full throttle when driving -30Hg.

5.) no fault codes on the system, no issues as you would expect and drives to me, normally. But is quite rumbly

things i have done to the car to try and remedy the situation.

1.) replaced a hand full of vac lines to the, anti shudder valve, turbo solenoid ect. as they had worn through.

2.) I have checked the turbo solenoid and it is functioning under vacuum as to be expected and is not sticky.

3.) erg valve has been removed and cleaned up.

4.) i have bought a new MAP(presure sensor) but it hasnt arrived yet.

5.) i have pulled off vac lines to key components and i can feel it is sucking well


what do you guys think? anything you can suggest or had similar issues for?
weird that the car drives as you would expect but the obd registers no vacuum readings?
is the loose nipple on the vac pump to be an area of concern?

any help will be greatly received.