The igniter and coil earth through the cage that holds them on the rear firewall.
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Worth checking that's still making a good connection.
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Some people run a second earth just to be sure.
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Do you have error codes 21 or 25? Both are lambda related.
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Also, check your exhaust system, the b-pipe in particular because I've had holes in mine before the O2 sensor and it does overfuel then.
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Taking the heatshields off can be a pain but the last two have cracked right on the two-into-one join.
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