I recently noticed that boost was falling off at the higher RPM's and suspected a boost leak. All I wanted was 15psi throughout the powerband on my S16G turbo, but was seeing the boost fall from 15psi to about 12psi by redline. Hooked up my boost leak tester and heard air leaking out around the TB.

We all know that the TB shaft on pretty much every TB leaks, but this leak sounded substantial so I went ahead and changed out the TB gasket, hose clamps, and silicone coupler.

Before I had the idle set screw turned slightly in and the car idled perfectly at 800 RPM's, now I have it fully backed out (butterfly plate as closed as it can get) and it idles at 1K. Also, when I am in neutral and coasting to a stop, the RPM's jump up and sit at around 1500 RPM's, and only fall back down to 1K when I come to a full stop.

Took the car out tonight and did two 3rd gear pulls, and the boost issue seems to be worse now. On both pulls I had the initial boost shoot up to 14.6, and by redline it had fallen to 9.2!

I am running a Joe P Pro Z MBC. Any ideas guys?

1999 Eclipse GS
Built motor
Hahn 16G Turbo w/ FMIC
Hahn Stage 5 Portfueler (270's & 500's)
Zeitronix Zt-2 wideband w/ 3.5bar MAP
3" SS Turbo Back
CM Stage 4 Clutch and Fidanza Flywheel
Baer Big Brake Kit