A bit of brain teaser this one. At around 2500 RPM, either static or driving, the engine surges slightly. You can feel it when driving. I think we're the third garage to look at it so far, so it would be good to get to the bottom of it.

I've posted a link to a video on YouTube below as I think this is the easiest way to demonstrate what its doing.

You can see from the video that MAF readings and boost pressure increase and decrease with the engine rev's. I've also noticed that the EGR operation is going mad. This fault stops if we unplug the MAF sensor or the vacuum pipe to the turbo actuator. A previous garage has replaced the EGR valve and the MAF sensor. The vacuum to the turbo actuator remains constant, as does the feed back reading from the turbo.







Any thoughts?