sti engine issue

[Jmk]

hi i have a mark 1 sti impreza it has been off the road for about 18 months i would run the car once a week on a small piece of land recently the engine has been playing up i would draw of with the turbo starting to spin at roughly 2000 rpm it would gradually build boost then at 4000 rpm it should full boost with a bit of shove (320hp/fpt and 1240 kilos) but basically at 4000 rpm the engine would build no more boost and it felt like an NA engine however it did full boost when i did a 5000 rpm launch more recently i started her up and was soon smelling a burning type smell on idle if i give the car a few revs (say 2000) after about 10 seconds i see smoke/steam coming up through the offside bonnet vent this goes away if the engine is idling i had a look in the engine bay and couldnt see anything wrong prehaps mice eating wires or ? anyone with a idea ? i can post up the engine mods if that would help cheers

[Jmk]

hi i will do those checks and have somebody look for a leak tommorow

the engine mods are
apexi cone induction filter
uppipe
modified fuel pump
FMIC
breathers
omega pistons
550 injectors
tubular headers
full RCM 3 inch system with prodrive backbox
HKS ssqv bov
car was mapped by duncan @ race dynamix
more than 1 person has said the car makes around about 320 hp the standard turbos limit