If you have a boost gauge it may show up as fluctuating boost as it does it, really is an easy job to do the waste gate arm, the ball ache is taking the turbo shield off which is a pain on its own, but you also have to take off the intercooler (I think) to get at it, I suppose the other thing it could possibly be is the boost solenoid and restrictor pill, maybe both could do with a clean with electrical contact cleaner, there's stuff on google for the doing of above operations, basically just connect your green connectors together under you dash/steering wheel/foot pedal area once you've removed solenoid, taken pipes off (remembering which goes top/bottom, with the connectors connected and ignition on the car will start cycling the fans and that solenoid will continuously open and shut, while its doing that you buzz the cleaner through it, and restrictor pill is in pipe coming from turbo snail (I think) and pipe needs to be removed and cleaner squirted down there to clean the pill/brass restrictor