Originally Posted by
Dicko&Sarah
Right I've tried it today a by easing the throttle in 4th and 5th and I've also tried it with vacuum pipe from boost controller to turbo disconnected, and yep its still the same grrrr
well it looks like a boost leak of some sort then. If you have taken the boost controller out , there is no way the ecu can be cutting the boost electro/mechanically. Lot of mention about the dump valve from others above. Have you removed it to see if its split.
For you to loose 1/2 your boost it must be a huge leak in the TB??

When you loose the boost how does the car run? Rough or quite well considering?
More importantly, how did you do the leak test and what pressure did you use.