Injector loom is a known and common fault on these engines. He may well have "tested it", but I'm betting there's an intermittant fault in the loom. It rubs against the stupid plastic engine cover and the wires degrade inside due to the rubbing and vibrations.

The other thing you're describing sounds like the swirl flaps. These are a common fault on this engine too, they gum up and fail. The fix is to replace or remove, both method need the inlet manifold removed which is a BIG job. Took me and a mechanic friend an afternoon to remove mine, strip the swirl flaps out, cleaning the inside of the manifold, and blanking off the EGR valve, then getting the EGR mapped out through a remapping company.

To be honest, the 1.9CDTI is a pup, especially in 16c 150hp guise. EGR faults, injector wiring, injectors, water pumps failing and flinging the timing belt. My best advice is get rid before you end up with an expensive boat anchor.

Speaking as someone who worked in a Vauxhall dealership for 15 years from 1980 to 1995 I personally think the Vectra C is close to the worst car Vauxhall have ever built. Even worse than the FD Victor.

The best car was the 1982 - 88 Cavalier, especially the 1987 facelifted models, but they're rarely seen these days more's the pity.....