I once had a Subaru Turbo that had a wastegate stuck closed. It sure worked well...right up until the knock sensor kicked in and saved the engine by killing the fuel. Once it spooled up, it would repeat this power on/off every second or so until I took my foot off the floor.
I freed-up the wastegate, and though it didn't have the kick it had, it stayed together.

Holding the wastegate closed will build too much boost. Of course holding it open will build no boost.

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1991 GMC Sonoma Ext Cab w/Isuzu diesel (converted March Mar 2003) - sold
1994 S10 Ext Cab w/Isuzu diesel (converted Mar 2008)
1998 Toyota Sienna XLE
B6100HST Kubota CUT DIESEL

1994 S10 with Isuzu diesel and 5spd
http://img.photobucket.com/albums/v6...S15/SigPic.jpg