Q: 04 cvpi started running lean after changing spark plugs

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My boyfriend recently changed my spark plugs, and now my car is running like crap. I bought an obd 2 scanner and it's showing codes saying that my car is running lean. What is going on?
My car has an automatic transmission.

Check to make sure the plugs are tight but do NOT overtighten them. Use a calibrated inch pound torque wrench only; if oil is on the spark plug threads, request assistance from a mechanic in tightening the plugs because the oil throws off the torque readings and that can cause overtightening of the plugs. The lean operating condition might just be a coincidence insofar as the nearness of occurrence to the plug replacement. The specific code(s) you have downloaded would be used by the mechanic to narrow the diagnostic but typical causes of lean operation are a faulty fuel pressure regulator, a weak fuel pump, a clogged fuel filter, a faulty powertrain control module (rare), a vacuum leak, faulty injector(s), faulty oxygen sensor(s), and/or a faulty mass air flow sensor. If you want the necessary diagnostic steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a check engine light diagnostic and the responding certified mechanic will get this taken care of for you.

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