I've had this on our E46 325 - same engine (save for capacity....) as the 330i petrol. there's an amazing You Tube guide showing what to change by a guy called the 50sKid - will see if I can find the link.

Anyway. I changed EVERYTHING as the entire car was quite neglected by my GF before we met. Likely culprits - in order - are:

1) Main intake boot - in the pleats/where the smaller side hose attaches

2) DISA (which sounds like it's now sorted - there are various ebay O-rings for sale which you can use if you remove the one you have again (the integrated orange seal needs to be scraped out with a pick first though)

3) Vacuum lines off of the oil separator into the dip stick, and general oil CCV system

4) An easy one to check (which isn't obvious) and which ended up with brown pants moments on the motorway for me - the venturi hose on the brake booster. )The unit is sealed (plastic welded at the factory) - but the lid can separate - it connects the hard pipe from the brake servo/booster to the inlet. The pipe runs across the top of the engine with the wiring harness and fits into the venturi pipe I'm referring to just by the inlet. Worth a visual check.I'd lose servo assisted brakes intermittently - as the lid to the venturi pipe separated and then reseated itself - it fell apart in my hands when I inspected it again.......

https://www.bimmerfest.com/forums/sh...d.php?t=578766

5) check the fuel filter - it has the regulator built in or attached to one end - and the regulator has a vacuum line which is runs in to a very narrow gauge hard pipe. The hard pipe runs from the regulator to the manifold - but it connects via very short and narrow lengths of vacuum line and these perish and can tear. Again a few guides on you tube to replace - but is cheap and easy (just the way I like...)

Best of luck...