Excessive gas use

[gideon1331]

My Mother's '95 Avalon is having a problem with excess gas use.

It is a problem that has been gradually getting worse over time. Recently it has started getting worse much faster. There have been no check engine or other trouble lights.

Current mileage is 16-18MPG combined. My mother drives like a grandma and used to average 28MPG using premium. The exhaust is noxious and is hard to bare if the car is sitting still.

The car currently has around 275,000 miles on it. It had one O2 sensor replaced at around 180,000 but the other 2 are original. Can a bad sensor cause this much of a decrease in mileage without throwing a code?

The plugs/wires are pretty new. Replacing them didn't help.

We had to dump extra ethanol in the tank to get it through emissions. Hydrocarbon emissions were 200ppm (the limit). The test before that it was 199 and I had just seafoamed it.

Any ideas? Otherwise the car runs perfect.

[ImDisaster]

Could be the EGR, though that should throw a code. Could be the head, lost compression...is the exhaust white (water vapor.) Is it losing radiator fluid?

[gideon1331]

We did check the EGR based on the service manual (we have the official Toyota one) and it passed with flying colors.

Nothing white (or black) in the exhaust. No fluid loss whatsoever...it doesn't even consume any notable amount of oil.

[ImDisaster]

Originally Posted by gideon1331

We did check the EGR based on the service manual (we have the official Toyota one) and it passed with flying colors.

Nothing white (or black) in the exhaust. No fluid loss whatsoever...it doesn't even consume any notable amount of oil.

When is the last time she changed the plugs? Old plugs can cause poor ignition...same thing can happen if plug wires get worn. Does it idle well....high or low? Could it be a choke issue.

[gideon1331]

The plugs were changed at 220k - Denso Iridium's. The front bank of them have been pulled recently and they still look new. The wires were also replaced then and are in excellent condition.

Idle is the same as it was when we got the car with 146k on it. Starts with a slight bump of the starter and idles like a dream...just with putrid exhaust.

It did have a problem dying at idle about a year ago. That was caused by buildup in the throttle body. That was cleaned fully, but the mileage/emissions problem started long before that. It's just gotten to the point now where the decreased mileage is rather worrysome.