Hey, sorry it's taken so long to get back. Work, work and work. Busy time of year.
Probably the quickest way your going to find out what might be causing the problem is to put the car on an engine analyzer. Not real sure what that will cost up in Canada. There could be a number of different things causing the problem with power loss and fuel consumption. Did you have to splice the O2 sensor wire for reach on the header? If so, more resistance is going to tell your computer that a lean situation is occurring and then tell the fuel system to dump more fuel. Very noticable on a 4 cylinder motor.
With all of the sensors and relays on cars today gone are the days of doing things correctly in your own backyard. Check with the dealer, they might be able to supply you with the proper resistance reading on your O2 sensor. Try and get the EGR valve working.
If you want great power gains and have to get into modifying your computer, you might be better off going to a larger or turbo charged engine. The 2.3 is not a power monster. It will do the job it was intended to do for several hundred thousand miles if cared for, but it's no racer.
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