Car Juddering
 

I have a 99 wrx. I have recently installed a bigger intercooler from a 2005 wrx with a blow off valve. That was about a month ago. Since then I started to notice that the car is acting funny. at higher speeds I could see that the car is suddnely cutting off fuel as well as shaking a little bit. I took it in for a check and the boost was to high. we found a loose hose near the turbo, fixed it and that fixed the problem of fuel cut. Now the turbo boost is to low, and the car is shaking almost at all speeds and all gears and when I leave it in gear and let go of the gas pedal I can hear these explosion type sounds coming from the exhaust. It was checked out on the computer and everytthing is ok, so no MAF or other sensors problem. Please advise as I am from Poland and in my city we do not have a lot of subaru experts and the dealer already took a 100 pounds for basically nothing.

Has anyone done an exhaust gas analysis, atleast that will give you some idea of whats going on, i.e.over/under-fueling..