turbo problems!!

hi there, new in today!!
i have a 97` chrysler voyager with turbo prob`s.
when you get to about 150kms the turbo stops pulling, then refuses to work.even if you drop the clutch and let it idle.
then it decides to work.bit dangerous when in the fast lane over taking spanish trucks on the n10.....no power.....
i found a unit under the bonnet on the drivers side. with two 4mm black pipes into it.it also has a plug with four wires into it.
when i bought the car one of the pipes had been left off... the turbo was going real good at the expense of the fuel econ`.
so i reffitted the pipe and restored the economy.
then the problems started.
one pipe goes to the brake servo` and the other to the turbo activator i think? it continues to suck air after the motor stops running!! is this right??
also who makes the diesel engine for the european chrysler`s?
coz i thought you guy`s mostly ran the big petrols.
thanks for copping a look at this for me and any help would be appreciated.
anyone??
any ideas??
no??
someone??


please!!!