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My Corolla increases RPMs when I want to coast

My 2009 , 1.8 Corolla gets terrible gas mileage. 23 city (lowest was 12), best ever was 30 highway. I have approx 14K on the odo because the MPG makes me want to leave at home.

The MPG has been verified in writing by 2 different dealers, so I do not consider myself the problem.
I drive conservatively and calculate MPG based on actual miles / gallons.
Toyota Corp did not bother to fix this issue.
It has been serviced regularly and had whatever fixes Toyota offered.

What I think is causing my terrible mileage is some glitch in an engine sensor that causes it to rev from 900 to 1100 RPM when I take my foot off the accelerator and attempt to coast. The revs go down when I press the brake. This happens constantly, especially at around 25 MPH. If I do not brake, the car will pull for a while without slowing down like normal cars.

I showed my Toyota dealers but they all said nothing is wrong.
My Corolla even went up a slight hill without my foot near the accelerator.
One tech told me the Corolla is burning off extra fuel, but my car will pull itself for over 1/2 mile, too much time for “burning”

Something IS wrong. I have driven dozens of vehicles and never had one jump like this.

Anyone else have this issue? Any ideas on where to start diagnosing?

My Corolla is out of warranty so any repairs are out of my pocket.

Thank you.

Well if you were not out of warranty I would definitely recommend a dealer fix. Now we have to turn to black magic, If you are lucky a treatment of SeaFoam will help. Any engine lights?

Is the Overdrive turned off. When the Overdrive is off the logic system uses engine braking and downshifts to reduce speed. The downshifting pushes the rpms up. Can you feel the sensation of the transmission downshifting?

Overdrive is not off, I always drive with it on.
RPM revs happen when A/C, heater, defrost, most everything OFF except the radio.
Car is in D, not 3rd (very easy to slip)

No engine lights, dealer would have noticed those.

I have tried several attempts with fuel injection cleaner, MPG goes up a smidge, but back to terrible mileage and coasting.

You could check the fuel pressure. High fuel pressure could cause bad mileage, practically pouring gas into the cylinders, causing it to rev higher.
Is the car hard to start sometimes, by chance?

check your floormat i believe the car a electric gas pedal. I would start over fresh do you know any one that owns the same car model year,engine, and trannsmission oe see if your local dealer has one you can drive to see how it behaves. I would talk with the service manger at your local dealer he hasw the power to help people with problems like this becouse your car has such low miles on it. buy the way how long has the car be getting poor milage?

I may be way off here, but the difference between 900 and 1100 RPMs doesn’t sound to me like a huge swing in MPG. Will that affect it? Sure, but I don’t think it would be enough to bring you down that far.

The idea about the fuel pressure (RemcoW) seems to make sense. Especially if the engine would be burning off extra fuel.

I would also recommend checking some of the other typical culprits for poor MPG. You said injector cleaner, for example. I’ve heard varying accounts of their effectiveness, but it certainly wouldn’t harm MPG. Other than that, I’d suggest checking the air filter, tire pressure, and I’m sure there are a few other little tricks.

Also, make sure to take that anvil out of your trunk. It makes more for the engine to pull! :smiley:

Make sure the throttle position sensor is working right.
Could be off but not enough to cause a CEL.