Lack of torque

[chrisp_8600]

Hi,
My Landcruiser 90 with the 3.0 1KZ-TE engine has a periodically failure wich is driving me just crazy:
At normal the car is running smooth and quiet with a lot of power, but sometimes (more and more often) it gets a more noisy and vibrating idle
and when driving there is a significant drop in torque especially below 1600 and above 2400 rpm.
I wonder if this could be related to an intermitent hanging wastegate or some other trouble around the turbocharger.
Yesterday the engine was fitted with new nozzletips.Didn't solve anything.
Any help would be apreciated.
/LC