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#2: 02-06-2013, 08:08 AM
Title: Contributing V.P.
Location: Milwaukee
Car: 99 Legacy 2.5GT Toyota Supra 2jz/R154
Posts: 1,048
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Get a scan tool and check the o2 data. They both should sweep up and down @ idle and at 2500rpm should hold voltage steady. Also the front cat is a pre-cat and the second one is the main. Three causes are, bad or weak o2 sensors, bad cat or a exhaust leak by the cats. A exhaust leak by the cats will cause a false reading thus making the ECU think there's a lack of efficiency thought the cat. GL.