Out in my96 wrx v limited today. boosting fine and running well. Came off a round about in 2nd pulled out to overtake but but no boost. turbo gauge was saying its boosting at 1.5bar but just isnt pulling and goes all jumpy. Very odd.
Dump valve releases all the pressure as normall.

any help would be greatful

 

I have a wee problem with mine at times, but I do know what is causing it. The symptoms sound as yours are.....

I have an Apexi ECU with the Hand commander. I have the Temp reading on show on the hand commander. My ECU`s Temp sensor can play up now and then and gives a false temp reading to the ECU, sometimes showing -49.
This just happens for a second or 2, but it`s enough to make the throttle lumpy. The boost pressure stays where it should during this wee temprature tantrum and Dump Valve Blows off as normal.

Maybe it`s the ECU Temp Sensor like on mine. If you dont have a guage or Apexi + Commander you won`t know this is happening as the Temp guage on the dash board is running from a different sensor.

This doesn`t happen often at all with mine, but I know the problem, just awaiting on a new ECU Temp Sensor