[drunkenup]

On longer drives the car would slip into a poor running state, higher fuel consumption, the revs would hang, climb quicker per given throttle input, and become less precise. It would also struggle to hold an idle and most interestingly, slightly amplified intake noise in the mid rpm range. I modified the stock airbox to accept a cone filter so its a little louder than stock when it's running "correctly."

I rebuilt the DISA valve and doesn't seem like I've encountered that running mode since, except on this one occasion when the throttle symptoms may have returned.

Immediately after rebuilding the DISA the intake noise after ~3500 rpms became much more aggressive, exactly like the E86 3.0si's with the modified sound tubes... and then, the next day, suddenly the intake was as quiet as before again. But then, after clearing codes, I went for a spin and the extra noise returned. The exhaust VANOS code had returned. The engine has felt the same since the DISA rebuild, running fairly strong with very minor idle fluctuation. So, now I'm exploring a couple possibilities.

-Exhaust VANOS solenoid is jamming, exhaust cam is staying in full retard or advance, and somehow amplifies noise back through the intake
-DISA valve is still screwed? Don't think the position of that valve would make such a major change in the noise of the intake, though. It may have thrown a code again since the rebuild, will only know for sure if it comes back again.

How likely is the first scenario? I ask because this fluctuation in induction volume is so distinct and unusual. Sort of frustrating, especially since it seems the engine is running correctly when its quieter, what a tease.