misterious vacuum appearing when cold

[0-sparx-0]

i have a 1990 2Lt 2.4 turbo diesel surf and when i start it from cold it wont boost, and when holding at a continuous rev eg 2000 rpm the boost gauge alternates from vacuum to 0psi on and off and almost sounds like a flap is opening and closing or something, but once its warm it's fine, any help with this would be very much appreciated.

[cataclysm]

When the engine's not under load, you wont get boost below 3500, and you shouldn't be going that high without load anyway.

What you've got sounds a little like damage to the high-pressure end of the intake ducts, or could be a faulty sensor.

I'm sure the more experienced guys will be along later with a more definate answer.

[0-sparx-0]

hey mate cheers for that, i actually located the problem and it was the diafram that controls that little flap ontop of the inlet manifold to make the engine shut off smoothly.