I have recently purchased a 1995 Legacy twin turbo.
It has HKS FCD and AFR as well as HKS EVC for the turbo.
I drove the car for about 1000kms with a mild sort of missfire when at low revs about 2000rpm under load as soon as over 3000rpm everything smoothed out and the car pulled very well all the way to 7000rpm. Now driving yesterday at about 180 kms with turbo boost up to about 0,6 bar the car developed a serious loss of power and started back firing through the air cleaner and also a bit out the exuaust. If i drive very causiously the car goes well but as soon as i push the loud peddel it looses power and misses.
When the car is standing you can rev it with no problem it only happens under load .I have also fitted new spark plugs. Please any advise would be welcome

 

Could be coil pack breakdown,after those have been checked/replaced.

I'd then consider air mass flow sensor

After that take it to a specialist for a good check over