Need help tuning a 3 port boost solenoid

Need help dialing in my 3 port boost solenoid on a 2007/2008 wrx using ecuflash. Ran fine with the stock 2 port but as soon as i installed the 3 port it has a stumbling affected on the vehicle more so at low rpm. I reduced both proportional and integral gains by half but still no luck. No fuel maps or spark maps have been changed. Any help would be great

99 percent of all cases the problem is with proper hoses connection...

That what i throught as well. Have check the lines to where they go and tripled checked them again. Pictured is the solenoid im using and the way its configured. Peirburg 3 port.

What solenoid are you using? Have you done a bench test on it?

Maybe during installation something else came loose - it needs to be double checked. I spoke with Subaru guru and he recons that installation of 3-port solenoid wouldn't have any impact on engine stalling...

Reinstalled the factory 2 port solenoid with the factory boost pile and the factory base map but still getting stumbling little more so in 3rd gear not as bad bit still there also when its cold. Also smoked the manifold and no vacuum leaks was found. The engine was rebuilded 4,200km using a stock ej257 bottom end and ej255 cylinder heads with port work and 1mm oversize inlet and exhaust valves. Could the Volumetric Efficiency be playing a part in this stumbling? All the maps are set to factory subaru base maps.

Definitely ported heads and bigger valves are playing major role in that situation. Most likely you made ports bigger which caused the air to loose its velocity at low RPM range... It's always vthe same with tuning - you are improving one thing but hurting another...

Thanks your help Shota MAKARASHVILI I think your spot on with what is happening. Would you recommend rescaling the maf? As well as the injector data as its out 25% as i found in injector latency and pulse width? Using ecu flash and romraider.

I'm not sure how it works on Subaru as am from Mitsubishi world. I would raise idle rpm a little bit (say 850 -900), make afr 13.8-13.2 progressively in that area, increase ignition timing untill engine doesn't stall anymore...