When I'm driving my BNR32 at about 100kph/3000rpm I sometimes get what seems to be turbo flutter. It's not the stuttering noise that happens in some cars when you rev and back off. Mine is more of a steady beat that could be mistaken for the oosh oosh oosh at a dance club. It seems to happen more often going up hills, which is unfortunate because that's when I need boost. The noise goes away if I back off the throttle or give it more. It doesn't happen at any other speed or rpm.

As near as I can figure, it's something wrong with the BOV, but I don't know why it only does it at this specific speed and rpm. I wouldn't mind so much if I didn't spend so much time at 100kph/3000rpm.

The car has some mild parts. The previous owner told me he put steel guts in the turbos. It has a pair of Bee*R BOV's.

I read your post a few times through. Having a hard time fully understanding your issue. From what I understood is your having a surging problem under a light load. Most turbo cars i've driven have a mild surge throttle response under a very light load. Almost as if you either in boost or out of it. You can almost feel there is a definite flat area that if under a light load would be felt as a surge. That being said.

If it is violent like spill your coffee in your lap id say there is a number of things you could go after.

Id start with the basics such as battery alternator oil change checking for pending or stored ecm codes. Review service history put in some fresh appropriate octane fuel from a high traffic station. Then jump right to setting base idle and timing. Next verify your throttle position sensor is within its voltage range with no flat spots.

Compression test a boost leak test. Might just add engine and chasis grounds to supplement factory ones. Adding additional grounds helps most older vehicles.

After all that go back to factory recirc type "BOV's". Sadly if you dont recirc your bypassed air back to the turbo after letting off the throttle this will cause a massive "surge" and is likely part or your whole problems. This can be tuned out a but never completely in my experience.

I guess I could have started with the BOV but I thought of it after I typed all the other stuff......

Good luck!

Okay, so light surging is normal? It's my first turbo car.

Id say yes minor surge is normal during the tip between in and out of boost. Maybe ride in a model like yours that is say more stock. Maybe even another turbocharged vehicle. I suppose if you have nothing to compare it to then you would be oblivious if it were abnormal. I really cant answer that yes or no.