I had this fault when I broke my N112 valve. This is the valve which controls the SAI system. It lives underneath the metal plate which supports the dipstick shroud on the front. Two pipes go to it, one from the N249 which is a vac feed, and the other one goes to the combi valve on the right hand side of the engine. The combi valve is silver, and part of it is what bolts to the head of the engine.
The actual SAI pump is a massive beast that lives bolted via a bracket to the front of the engine.
To be fair, either way is is fine, removal or replacement.
Things to bear in mind.
1) You will need a blanking plate to blank off the hole in the side of the head. Available from Forge - not cheap for what it is though.
2) It is an absolute pain in the **** to remove. The pump, and the bracket which hold it on are a night mare to get off. You will also need to remove the N112 valve, and block off the vac feed from the N249.
Depending on what you decide, I believe I still have my SAI pump and combi valve somewhere floating about in GWO if you need it.
