Hi. I'm new to this forum, so please excuse if this post needs redirecting. Have recently been having boost problems with arosa 1.4 turbo following broken cambelt/headgasket replacement. This is the sawn down 3 cylinder pd engine, non variable vane, wastegate, pressure actuated turbo. Having changed two valves and damaged followers, headgasket and bolts etc (genuine) cambelt (timing checked several times) replaced all smallbore vacuum/pressure pipes, checked all boost/intercooler pipes for leaks/damage, new MAF, MAP, coolant temp sensor, N75 valve, all bosch/pierburg, removed exhaust and inspected turbo, wastegate sealing disc, pressure testing wastegate actuator (all looking and performing like new) the car still intermittently slips into limp mode, usually under load, when not limping goes like a train, throws up negative boost pressure fault code, cycling ignition clears problem. We have applied our combined knowledge of 93 years to this and are completley stumped. Any new input would be greatly appreciated.