tonemayne

I've got a 1996 ES300, and when I first got it, about six months ago, I was getting roughly 18 MPG, which I thought was bad. However, the months since then, its just kept decreasing, and I've got 11 MPG on some tanks.
I do know that the O2 sensors are coming up with errors, and so is the Mass Air flow sensor, but I've read things online saying that it shouldn't decrease your gas mileage that much.
Any Ideas? Has this happened to you?
Thanks.

AndyG

In that time since it was getting 18mpg, you didn't change anything on the vehicle like wheel size or anything? And the only codes are the O2 sensors and the mass air flow? I would start by fixing that just to see if it gives any improvement but that's about the best I've got. Hopefully one of the more knowledgeable guys will have some tips.

Oh and welcome to the site!

GEORGE_JET

The upstream O2 sensors can have a dramatic impact on your mileage, the mass flow sensor will also cause a significant drop. Since you just got the car six months ago, have you checked the spark plugs, and air filter? It could be time to replace them. If you do end up replacing the plugs, make sure that you gap them before installing them.

tonemayne

Infact, I think one of the upstreams is a problem. Thanks so much for your help, I'll be getting on that right away, as well as having my spark plugs checked, because that hasn't been done yet either.

VicsIS350

upstream O2 sensors? My 96 has 225k and since last week right before I changed air filter I've noticed my gas mileage being worse...after filling car up in just quarter tank I was amazed from above full I only managed 54 miles when on average I hit over 100....by about half I had 155 miles when usually I'm in the 200s already...I replaced plugs last year and every now and then I get a p0446 something to do with charcoal canister but if I warm up car like a few minutes it keeps code away.