Hose diameter
 

On my 87 td, there is a small piece of fuel hose next to the ip, im wandering the id of this?
Anyone know?

7.5mm

Get a couple meters to replace all the fuel hoses in the area. The hoses to/from the fuel heater are formed but you can make do with plain hose.

Sixto
87 300D

Be sure to get 7.5mm. I have been having really bad air leaks in my pre-filter, and I am 99% sure it is because I am using standard 5/16 hose (which is 7.9mm) and non-german clamps. The "correct" stuff should be here today!

One end on the plastic pre-filters that I use (Bosch) is slightly smaller that the other. I have played around with a spare, with hose, clamps, etc, and can still manage to get a drop in pressure when testing it with a mity-vac, despite numerous attempts at trying to get a good seal. I'm sure many others have not had this problem, but, just warning you..I guess I am unlucky with hoses :)