ive a 95 classic sti and the past few days its been building boost to 0.8 bar on the gauge but its holding back until the car gets up around 5500 rpm the it goes again but the boost seems likes its droping off .1 or.2 bar then builds back up?
ive checked for boost leak and these none
changed plugs
cleaned air filter and inlet pipes to turbo
ive made sure the wastegates free and working

could it be the turbo on its way out?

 

anyone?

 

check the coil packs for cracks.take the rubber ends of and havea good look for any hair line cracks

 

You may want check the compression as well and as big chap said above check your coil packs as they are prone to cracking where they meet up with the spark plug. Just pull the rubber boots back and inspect for cracks.