Boost/power troubles after EGR and/or new intercooler

[Hodge]

Just posting this up to see i anybody had similar problems and/or any ides what this could be ... I mentioned some of it in my diesel power intercooler write up last week so some may be familiar with my problem.
Firstly thanks a heap to Mudski for helping us out with trying different mafs and egr plates... Was over at his place for a bit last night talking s*** and throwing out ideas.

Flow of events...
Fitted up dawes and needle valve ages ago and the car ran like a million bucks after it. Then I dropped in a EGR plate. Had to wind down needle a tad, since it was spooling up a bit faster with EGR blanked. So had the car running flawlessly for about a month like this.

Then last week I installed a new diesel power re-cored and tig welded intercooler and at the same fitted up a catch can. The car ran fine for half a day or a day and then it turned to s*** ...

Basically what's happening is, it'll fly through 1st , 2nd and 3rd gear boost spooling up fine or quicker than usual and maxing out boost. Then in 4th the car begins to labour, and spooling up takes a little longer than usual. Basically, it's turbo lag. It does get there, but very slow. EGT goes sky high until boost picks up. The other thing is @ 100km/h where my cruising boost was around 10-11, now hits 17 (my max) as soon as i touch the throttle.

So the trouble is, if I wind down needle to fix 1st 2nd and 3rd, I'll make 4th much worse... If I wind it up, to fix 4th, the first 3 gears are terrible as it shoots to max boost in a second and the snail is spinning it's tits off for no gain...

The other little variable is... Up until I've installed the intercooler, I've had NO codes on the system. As soon as the IC was fitted, P0401 ( no EGR flow) code popped up. Which is common on the common rails after blanking the EGR. I'm just getting the code on scan gauge and no engine light.

Could this larger intercooler be messing with my head and just making the mid range gears and power more unstable ? Maybe the extra flow of air into the system, is somehow stuffing up the EGR valve? Also does this P0401 code do anything to the system like put car into limp mode or somethign, or is it just a warning.

I've began the process of elimination, took EGR plate off and re-fitted old gasket to see what happens to begin with. This will drop spool up rates across the board a little.

Any ides would be appreciated. The car as it is now is, not pleasant to drive. Very frustrating as I need the rig over the next few weeks to run well!