You don't say what kind of car you have. There is a hesitation problem involving the knock sensor on the 1997 and 1998 2.5 engines which results in power loss around 3-4k RPM.
The Subaru fix is a new ECU. There is an aftermarket hack floating around that essentially splices resistors in to impeded the line signal from the knock sensor to the ECU. I couldn't find the URL in a search. Gary's page appears to be gone.
Anybody have the info on this?
Here's more info:
[This message has been edited by gavin (edited February 01, 2001).]