Hi guys, not sure if it was in this thread or another thread but the this issue is a tuning issue where the exhaust cam phasing is too aggressive. Some of the Z33's that runs the VQ35HR have the same issues. There are a few tuners from UK and US who knows of the issue. One of them quoted this
"We see a problem on these car mostly at part throttle which is caused by the exhaust cam control issue , basically the PID (closed loop) is too aggressive and causes the cam to move too far causes a stutter it could cause the same issue at cold warm up I presume if it is using the same part of the exhaust cam map."
To test his theory, I set my exhaust cam phasing settings to 0 and I don't get any of these issues at all. This is of course a band aid fix as this means I won't be utilising cam phasing at all. Will need to get a tune done with someone who understands cam phasing and test how far we can push it. I could be totally wrong though...