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Just Bought '05 Corolla - Mileage Is Awful!


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#31 Accent 1ZZFE

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Posted 11 March 2006 - 09:17 AM

Congrats on the purchase, has it been serviced thoroughly? Log books can be easily made to appear if all servicing was done. It may have fouled plugs, a dirty MAF, throttle body, vacuum leak, air filter, poor quality fuel being used etc etc etc.

It could be an ECU prob, I think the best bet would be to put it on a dyno and measure AFRs or plug in a OBD tool to see if the car is running too rich from the ECU tune.

The dealer should have the software to reflash the ECU with the latest update program from the current model, if thats the case, good luck.

Edited by Accent 1ZZFE, 11 March 2006 - 09:18 AM.

#32 Bikeman982

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Posted 11 March 2006 - 08:08 PM


Interesting idea about the ECUs. According to my info, MT is always Denso, AT is either Denso or Delco. Furthermore, some Delco ECUs are non-reprogrammable.
I also have suboptimal MPG, get only 30 on hwy and 27 city with gentle driving. I will check my ECU and report back.

Maybe we should test this ECU theory. I have a manual so I assume I have the Denso. I get an excellent 37mpg combined. Is there anyone with a manual that is getting really bad mileage?

For autos, can some people report which ECU they have and what mileage they're getting?


Good question - everyone do an ECU check.
I have an automatic and all mine (including the many I have laying around in my garage) are all Denso.

#33 the99contour

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Posted 11 March 2006 - 10:56 PM

You guys realize that you can't just go around switching around ECUs in 2005 Corollas. They have the passive anti-theft keys programmed into the ECU. If you swap the ECU and don't have the dealer reasign the keys to the new ECU, THE CAR WILL NOT RUN. Also, I don't know if Denso ECUs and Delco units are interchangable without dealer help.

Another thing, the sticker EPA mileage is always over-inflated. To obtain this figure, they drive at 55 with no air in a closed enviroment with no crosswinds or headwinds. Drive in medium to heavy winds or above 55, or with air, and you probably won't achieve even near the EPA figure. My Dad gets 38 MPG highway driving my '05 LE Auto, but other people I know get 32 MPG, and 25 MPG highway. I have a Denso ECU. My car was built in March of 2005.

#34 Bikeman982

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Posted 11 March 2006 - 11:07 PM

The brand of ECU can be checked without removing it. Good point about swapping it out - should not be done without knowing what effect it might have. Our intent was just to identify brands and compare gas mileages to see if there is a trend or pattern.

#35 gvr4ever

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Posted 11 March 2006 - 11:41 PM

You guys realize that you can't just go around switching around ECUs in 2005 Corollas. They have the passive anti-theft keys programmed into the ECU. If you swap the ECU and don't have the dealer reasign the keys to the new ECU, THE CAR WILL NOT RUN. Also, I don't know if Denso ECUs and Delco units are interchangable without dealer help.

Another thing, the sticker EPA mileage is always over-inflated. To obtain this figure, they drive at 55 with no air in a closed enviroment with no crosswinds or headwinds. Drive in medium to heavy winds or above 55, or with air, and you probably won't achieve even near the EPA figure. My Dad gets 38 MPG highway driving my '05 LE Auto, but other people I know get 32 MPG, and 25 MPG highway. I have a Denso ECU. My car was built in March of 2005.


I and others have gotten the EPA milage and then some. While, I can't get it every tank due to driving too fast, too many short trips, ect. When we want, we can get a average of 36-38MPG and our record is 43MPG and that's above the EPA ratings. I do belive that the EPA ratings can only be had using summer fuel formulas.

#36 Bikeman982

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Posted 11 March 2006 - 11:47 PM


You guys realize that you can't just go around switching around ECUs in 2005 Corollas. They have the passive anti-theft keys programmed into the ECU. If you swap the ECU and don't have the dealer reasign the keys to the new ECU, THE CAR WILL NOT RUN. Also, I don't know if Denso ECUs and Delco units are interchangable without dealer help.

Another thing, the sticker EPA mileage is always over-inflated. To obtain this figure, they drive at 55 with no air in a closed enviroment with no crosswinds or headwinds. Drive in medium to heavy winds or above 55, or with air, and you probably won't achieve even near the EPA figure. My Dad gets 38 MPG highway driving my '05 LE Auto, but other people I know get 32 MPG, and 25 MPG highway. I have a Denso ECU. My car was built in March of 2005.


I and others have gotten the EPA milage and then some. While, I can't get it every tank due to driving too fast, too many short trips, ect. When we want, we can get a average of 36-38MPG and our record is 43MPG and that's above the EPA ratings. I do belive that the EPA ratings can only be had using summer fuel formulas.


I would be very happy if the car I was driving got 36-38 MPG.

#37 gvr4ever

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Posted 12 March 2006 - 12:14 AM

BTW, I have a 05 5sp. That does make a little difference. I also have a TRD air fitler and I run Mobil 1. Everything else on the car is 100% stock. I think it is important to keep the car as uncluttered as possible. You can't get good milage with a loaded trunk, or having too many people in the car.

#38 bleo

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Posted 12 March 2006 - 06:34 PM

You guys realize that you can't just go around switching around ECUs in 2005 Corollas. They have the passive anti-theft keys programmed into the ECU. If you swap the ECU and don't have the dealer reasign the keys to the new ECU, THE CAR WILL NOT RUN. Also, I don't know if Denso ECUs and Delco units are interchangable without dealer help.

Another thing, the sticker EPA mileage is always over-inflated. To obtain this figure, they drive at 55 with no air in a closed enviroment with no crosswinds or headwinds. Drive in medium to heavy winds or above 55, or with air, and you probably won't achieve even near the EPA figure. My Dad gets 38 MPG highway driving my '05 LE Auto, but other people I know get 32 MPG, and 25 MPG highway. I have a Denso ECU. My car was built in March of 2005.


The intention is not necessarily to swap the ECU ourselves. However, if we find a trend that people with auto transmissions and Delco ECUs get really bad mileage, then we may have the basis to ask the dealer to change it under warranty.

And yes, I understand that EPA mileage is a test that is good for comparing cars to each other, but may not represent the mileage that you get in real life. In fact, the EPA already applies a fudge factor of -10% city/-22% highway to better represent real world numbers. However, it seems that this may not be enough to represent some American drivers! :P

You said yourself that your 05 auto Denso gets 38mpg highway (which is actually EPA), while others get 32 or 25. What we are doing is a like a 'case-control study' if you are familiar with the types of medical trials :). Basically, if a group of people gets good mileage (mid to high 30s), while another group gets bad mileage, what are the differences in their past that may have caused this? (ECU?)

Edited by bleo, 12 March 2006 - 06:48 PM.

#39 Bikeman982

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Posted 12 March 2006 - 06:49 PM

I think it can be determined that with all other things being equal, if one brand of ECU gets better gas mileage than another, that the ECU which is better may prove to be the best choice as far as gas mileage is concerned. I for one would try to get mine changed.

Edited by Bikeman982, 12 March 2006 - 06:49 PM.

#40 Mins

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Posted 14 March 2006 - 04:01 PM

Ok, I tried checking my ECU this evening by removing my glove box compartment. I did locate the ECU, but I could not identify whether it is made from Denso or Delco. It didnt say on the visible part of the unit, so this weekend im going to literally take off the ECU and check it out that way. To tell you the truth, By comparing what I saw with the picture from the repair manual, mine looks like the delco one :(
Still, I can't be entirely sure yet.
I took some pics too
This is with the glove compartment removed The white "Toyota Denso 5"sticker is for the cabin fan, not the ecu.
My pos camera couldnt focus.. this is supposed to be the ECU located near the bottom
This is underneath the ECU, all it says is "Toyota Computer, engine control" and some numbers.

Edited by Mins, 14 March 2006 - 04:02 PM.

#41 Bikeman982

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Posted 14 March 2006 - 08:27 PM

Ok, I tried checking my ECU this evening by removing my glove box compartment. I did locate the ECU, but I could not identify whether it is made from Denso or Delco. It didnt say on the visible part of the unit, so this weekend im going to literally take off the ECU and check it out that way. To tell you the truth, By comparing what I saw with the picture from the repair manual, mine looks like the delco one :(
Still, I can't be entirely sure yet.
I took some pics too
This is with the glove compartment removed The white "Toyota Denso 5"sticker is for the cabin fan, not the ecu.
My pos camera couldnt focus.. this is supposed to be the ECU located near the bottom
This is underneath the ECU, all it says is "Toyota Computer, engine control" and some numbers.

Thanks for the pictures. I can't tell what brand you have. Fortunately for me, mine all say the brand on the sticker. Maybe you could research the numbers on it??

#42 joshodonn

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Posted 17 March 2006 - 11:02 AM

I have an 06 manual CE... I drive it 20 miles each way to work at least 6 times a week and it's about 50% interstate and 50% city streets.... I had been averaging about 30-31 MPG.... This last tank I used Chevron 87 grade fuel, added a bottle of Chevron fuel injector cleaner, and bumped my tire inflation up to 36 psi (was around 31)... I filled up this morning after driving 355 miles and it took just over 10 gallons, so these small changes increased my mileage by almost 5 mpg. I realize this is only one tank but I'm optimistic that the increased efficiency will last.

#43 gvr4ever

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Posted 17 March 2006 - 07:03 PM

I have an 06 manual CE... I drive it 20 miles each way to work at least 6 times a week and it's about 50% interstate and 50% city streets.... I had been averaging about 30-31 MPG.... This last tank I used Chevron 87 grade fuel, added a bottle of Chevron fuel injector cleaner, and bumped my tire inflation up to 36 psi (was around 31)... I filled up this morning after driving 355 miles and it took just over 10 gallons, so these small changes increased my mileage by almost 5 mpg. I realize this is only one tank but I'm optimistic that the increased efficiency will last.


Why did you use fuel injector cleaner on a brand new car?

#44 Bikeman982

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Posted 17 March 2006 - 10:56 PM

I have been getting only 25 - 27 MPG and I am driving 100 miles per day. I don't think that is very good. I have the 1.8L 7A-FE engine and I really like the power that it has. My wife's car has the 1.6L 4A-FE engine and would probably get better mileage. Maybe we can trade??

#45 joshodonn

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Posted 20 March 2006 - 04:56 PM

Why did you use fuel injector cleaner on a brand new car?



That's a good question.... Although it is a 2006, I've already managed to put nearly 10,000 miles on my vehicle and have been guilty of purchasing gas that may not have been of the highest quality. Therefore, I used a bottle of injector cleaner to remove any build-up that may have occured to date...