My '97 Passat has set 2codes - p0605 & p0101. It's power/boost is erratic. Many times revving above 2500 rpm will fix the problem, but not always. It will also surge under load sometimes. I've checked and cleaned the air filter housing. It has the Pierburg maf, which from my my Internet reading is usually not the issue. I haven't replaced the ECU internal hose. That's my next step. Any thoughs or suggestions would be appreciated.