On turbo cars, a boost gauge is handy. An accurate one will even tell you what boost you're running! Even a fairly cheap boost gauge is (To me) as necessary as an oil light - it tells you when somethings up with your engine.

When, one day, your Impreza stops boosting as far as it did before, it could mean many things - You put rubbish fuel in it and your ECU has backed the ignition and boost off to save your engine, your mass sensor is kapput (Or just dirty), you've melted a piston or many other problems.

Put some fresh VPower in it, fix the prob, reset the ECU (l leave the battery off overnight to do this), then drive it (Fairly hard at first so the ECU gets the idea).

Question is this:

What did the problem turn out to be when your turbo stopped boosting as high as before?

Hopefully you've had this a few times and have some goodfor me. I am compiling a list for myself and will send it to all the Impreza owner sites l know if l end up with a good list :)

Thanks in advance
BTW - PLEASE no speculation - actual experiences either you or a garage have fixed or diagnosed for certain. Thanks
EDIT ->> Re: Resetting Impreza ECU:

This link:

http://scoobypedia.co.uk/index.php/Knowledge/ECUReset

describes, in enough detail to be credible,how to reset ECU is on various Scoobs... I am now thinking disconnecting the battery might not be enough to genuinely start the ECU learning process from scratch - it might do but possibly not. One mate told me to disconnect battery terminals then touch them together to drain capacitors... Drain caps, Yup... Touch terminals (Making sparks and surges)... er... no... He works on Land Rovers... Maybe they're used to that sort of treatment, lol.

the tube between the inter cooler & the intake manifold, was not tightened down after l changed the clutch,

the small tube from the waist gate to the turbo output had fallen off the control solenoid, (it was my fault)

and on a turbo mitsubishi (not a WRX), the bolts on the turbo to the exhaust manifold came loose about a 1/4 inch.

l have speculation for things that almost happened to my WRX that would have caused this, but u said that u do not want speculation, so email me if u want that info.