[Capital Punishment]

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A sidenote, we figured a few months ago that the car ran rich when we changed the spark plugs b/c we had to pull the intake manifold off and discovered a lot of carbon build up in there, which we cleaned out.[/b]

I dont think you were necessarily running rich just because there was carbon buildup in there, carbon buildup is normal, especially with that many miles.

Also, there is a bench test for an oxygen sensor to determine if it is working properly or not. Someone will probably post it, if not, PM me and ill be able to find it. The cats shouldnt just up and go bad, though.