This is more of an info post to people who may have had similar problems to me.
The problem was after an extremely heavy and sustained downpour of rain whilst driving about 500kms, and the rain pouring the whole time, all of a sudden at 2500rpm, the engine would not rev any higher. It appeared that the turbo wasn't kicking in. Drove the last 200kms home without a turbo only able to go 85km/h and unable to accelerate at rate which would normally kick the turbo in or the car would essentially "choke". Similar to when u redline and the engine stutters.
I took the car to Nissan servicing in North Melbourne and was told that there was an error code on the air regulator. It was apparently refurbished and worked ok, but would make a slight stutter at 2500 rpm's as the turbo kicked in.
2 weeks later another heavy downpour of rain and the same issue occurred. Went to Nissan servicing and they then "cleaned" the regulator.
1 month later same thing again. I finally had some time so cleaned the air filter and air flow meter just with air compressor. Temporarily fixed problem.
2 weeks later another downpour and same issue again. I again cleaned the air filter and airflow meter, this time with WD40 in the air flow meter. Next day took apart the AAC (the bit with the idle screw in it). It was completely caked black inside. Cleaned this with WD40 and cotton buds. Put everything back together and the car now perfectly idles, no stuttering at 2500rpms and smooth acceleration.
My question and theory is that with the heavy rain, mist was getting thrown up under the car, getting through the pod filter, clogging the air flow meter causing a short, and also making the AAC spring and piston unworkable. I have no idea what part nissan servicing actually "refurbished" because it definatley wasn't anything i cleaned in the last few days.
