what should i check or do? already tried fuel injector cleaner from STP. and also what exactly is a leak detection sensor and where is it located ? thank you.

passing smog is a bish

A bad upstream o2 sensor can cause you to run rich.

Replace spark plugs and wires, maybe the fuel is just not burning off like it should?

unless you have had the battery disconnected recently and your car hasn't had a chance to learn the fuel curves again. or if your at WOT its gonna be rich.

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