Q: my gas mileage is decreased and i have random misfires, noisy lifters when cold but noise goes away once fully warm . o2 sensor?

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My gas mileage is significantly decreased Im getting error code p0300..random misfires. Cars lifters rattle until the car is fully warmed up and then the noise goes away. No performance issues however. dtc reads error code 1349...random misfires again. Oil pressure was checked and confirmed oil pressure is goodm also, when the car starts it idles high at 2000 rpm, once it warns up idle is nornal . Ive done considerable research into this and have determined its probably the upstream o2 sensor. Its probably not an actuator problem because there are no performance issues. Also its probably not a wiring or coil issue because the misfires are random. When this problem first started i could smell gasoline right after start up, but once warmed up the smell went away...finally, i have purchased a new upstream 02 sensor, but when i asked a shop to install it, they gave me the run around and said it wouldn't fix the problem. My research has revealed these are the symptoms of a bad o2 sensor

My car has 132000 miles.
My car has an automatic transmission.

Hi there. Thanks for writing in to YourMechanic.com about your issues the Toyota is experiencing. It is possible that you have two, independent problems that are causing two unique symptoms; the random misfire and the fuel economy issue. Although faulty O2 sensors may impact the fuel efficiency of your vehicle, it is highly unlikely that it’s the source of the misfire. However, the P1349 OBD-II code on a Toyota is typically due to a oil control valve or VVT solenoid issue. This would cause the misfire and possibly the rattling on top of the motor. You should watch this video as it’s very well diagnosed and explained - perhaps this will resolve one of the problems.

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