ghbogen

I own Lexus ES 2001 with 79000 on the odometer..I was usually getting 20-22 miles/gal but in the past few weeks it suddenly changed and the gas consumption increased to 12 miles/gal.
My driving pattern did not change,My tires have a recommended air pressure.My spark plugs were changed few months ago.
My car starts and drives well.Good acceleration.
I understand that one of the frequent reasons responsible for a poor mileage
is a defective O2 sensor.However no light appeared which would indicate this problem and my car passed emissions test ,which it would probably failed if there was a problem with O2 sensor.
Any suggestions will be appreciated.

Lexmex

Could be any number of things.

Generally when I get something that screwy, I'd be inclined to unhook the battery cables for a few minutes, put them back on and then go out on the highway for a bit followed up by a bit of street driving (about 15 minutes highway/15 minutes city). Another possibility (since no CEL) is you have perhaps a blockage issue with your injectors, so a good fuel injector cleaner (Redline Fuel System Cleaner is my personal favorite) could help there. Also a possibility is a dirty MAF sensor or air filter.

One issue you may also have up there is winter gasoline and MPG problems.

Finally it need be said, but check your driving pattern. Sometimes a bit heavier foot can lead to increased MPG. However, in your case, I don't think that's likely enough.

GEORGE_JET

when you changed the spark plugs, did you use the recommended plugs, and did you check the gap before installing them? Gapping the plugs is very important, and often overlooked. Also do you have a stock air filter. Some of the aftermarket OILED filters can be over-oiled, and the excess oil can contaminate the airflow sensor. O2 sensors should be changed at around 80k, so it is possible that this is a problem, (but chances are that you have other issues).

llcoolpass

I have the feeling the two experts before me covered a lot of good things, and may have covered this, but my first reaction is, is there something wrong with your mpg computer in your car? or are you doing the math like i do when you get a fill up?

PFB

Another possibility are stuck brakes. Make sure that you don't have a partially stuck brake calliper, or parking brake.

Test on a level road, with engine off, put the car in Neutral and give it a slight push. See if it rolls freely.

Takes 2 Minutes to find out.

Phil

ghbogen

Thank you for your comments and suggestions

MikeLex

Pls don't forget to give feedback when you get the problem fixed