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

asked by on

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.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. my gas mileage is decreased and i have random misfires, noisy lifters when cold but noise goes away once fully warm . o2 sensor?

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Arcing from distributor to valve cover

The coil is the only thing that is putting out high voltage. The ignition spark will always look for the quickest path to ground. This is the way electricity works. If you are getting spark jumping to the ground before...

Q: Engine swap details needed. I need to know if the swap will fit.

Hi there. When it comes to swapping engines for your vehicle, what you can do is check all of the engine mounts and transmission mounts and make sure that they will work. If the mounts are a little off but...

Q: How do I release the steering wheel lock with the key?

When your car is turned off, the steering wheel will sometimes lock as a safety precaution. During this time, the steering wheel will barely move, and the car cannot be turned on. To release the steering wheel lock, insert the...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.