I was wondering, does anyone know if the 2.4 159, has a recirculation valve in the turbo pipework?
If not, why not? surely thats just going to cause the turbo to die quicker if it's giving you compressor stall occasionally.
I only ask because I think thats what happens to mine occasionally, if i'm on a sort of low trailing throttle, and the egr has bled off all the boost, (you know when your pootling along at about 30mph, and the turbo gauge goes from the 1 notch to 0 and your mpg goes from 30ish up to 60ish) then you apply a bit of accelerator and then take it off then put it back on again, and then you lose power and note that the boost gauge is recovering back from zero.
It's the only niggly thing left with my 159, and i think it's either compressor stall, or if the recirc valve exists, due to it's previous egr failure coking the engine and valves up, it's also got gummed up and needs replacing.
I like your thinking, but your mixing petrol engines and old style turbo's with what modern diesels have.
The purpose of a dump valve is (as you say) to keep the turbo spinning during gear changes when you lift off, and the throttle flap is momentarily shut...but diesels don't have a throttle flap, the flap you may have seen is used to shut the engine down, we control engine speed with fuel on a diesel, to all intense and purpose the intake is wide open at all other times, no dump valve needed.
As CJ says, our turbo's don't use a waste gate either, boost is controlled by a moving vane system on the air compressor side in the turbo, all clever stuff and yes they can stick.
So this leads us to what engine you have, is it the 200 or 210hp engine?
If its the 200 then they do have a little more lag from the KKK turbo over the Garret in the 210. Other wise we are back to sticking vanes possible boost leak or the old favourite your egr valve is still playing up.