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Hi guys, I got a 2002 rav4 4 sp. It's got 166k miles and this past weekend I got an oil change, coolant change, and fuel system service. I began noticing that my mpg was getting worse starting about two months ago. I used to be able to get about 330-340 miles to the tank on the pure highway and about 300-320 in the city. I occasionally drive from Santa Barbara to the bay area to go home and that trip would drain the tank but wouldn't leave me empty. When I went home last month, I wasn't able to make it one fillup in either way. After the fuel system service this weekend, my mpg saw a major increase. But that was only for one day. I got almost 400 to the tank and that was driving from the bay back to Santa barbara. Now these past few days, my mpg has been really crappy. I used to get at least 160 miles before hitting half tank, now I barely make it to 130. Any ideas as to why??
TLTR
Been noticing that my mpg has been dropping(320 tank to 300). Did fluid changes and fuel system service and noticed mpg were up(almost 400 tank). The next day after the services, mpg is worse than before(130 half tank=260 full tank).
 

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The reduced mileage you're getting blows my best mileage out of the water. I have an 03 Rav 4 I get maybe 300km (~185mi) to a tank, 350 if I'm lucky.
I've ran about 5 bottles of fuel injector cleaner thru the system, both Lucas and Seafoam, with no luck. I changed my PCV valve and hose and that helped a little bit bringing the mileage from 200-250km a tank to the aforementioned 300-350km. I have also plugged an exhaust leak after the resonator, changed the bank 2 downstream o2 sensor, drained and filled engine oil and atf twice, checked for a stuck caliper, cleaned the throttle body, maf sensor, and idle air control valve, and checked valve lifter clearance. I have no engine codes and the fuel system enters closed loop after warming up. I've even busted out the stethoscope and listened to the injectors which sound perfectly fine.
The only issue left I can think of is the catalytic converter has a rattle at idle, but never under load, and that could possibly reduce airflow and cause slightly worse mileage. But even that shouldn't cause it to be anywhere near as bad as it is.
I've scoured these forums and others for a possible cause and haven't come up with anything.
I am at a complete loss with this. Please keep us updated if you end up finding a cause.
 

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Keep in mind I'm sharing advice or recommendations from a 2AZ-FE perspective, but our RAV4.2s still have more in common than otherwise.

1) My experience with unexplained worsening gas mileage has been attributed to slowly failing O2 sensors, on x3 different Toyota vehicles: x2 RAV4.2, x1 Tundra.
2) My alignment is readjusted every 3,000 miles . . . because it needs to be. That's how quickly they can come out of adjustment.
3) Tire pressures change with season. Pending no action by the owner/operator, they go softer in the winter, firmer in the summer.
4) On the subject of tire pressures, if your RAV doesn't have TPMS, be sure they aren't slowly going flat due to damage.
After the fuel system service this weekend, my mpg saw a major increase. But that was only for one day.
This is puzzling :unsure: A fuel system cleaner shouldn't be providing greater performance "during" the treatment. The combined chemical effects of PIB, PEA or PIBA should have the opposite effect on fuel burn: it's reducing the fuel's octane and introducing larger amounts of contaminated fuel. The benefit of a fuel system cleaner are realized "after" the treatment. This sounds like you got snake oil instead. What product was used for this?

Andeleon, I would recommend you replace the O2 sensors in your case.

The reduced mileage you're getting blows my best mileage out of the water. I have an 03 Rav 4 I get maybe 300km (~185mi) to a tank, 350 if I'm lucky.
I've ran about 5 bottles of fuel injector cleaner thru the system, both Lucas and Seafoam, with no luck. I changed my PCV valve and hose and that helped a little bit bringing the mileage from 200-250km a tank to the aforementioned 300-350km. I have also plugged an exhaust leak after the resonator, changed the bank 2 downstream o2 sensor, drained and filled engine oil and atf twice, checked for a stuck caliper, cleaned the throttle body, maf sensor, and idle air control valve, and checked valve lifter clearance. I have no engine codes and the fuel system enters closed loop after warming up. I've even busted out the stethoscope and listened to the injectors which sound perfectly fine.
The only issue left I can think of is the catalytic converter has a rattle at idle, but never under load, and that could possibly reduce airflow and cause slightly worse mileage. But even that shouldn't cause it to be anywhere near as bad as it is.
Sounds like you've done a good job covering the bases. I think your RAV4.2 is either running pig rich, or the engine is pulling a heavy load. I do 350 miles in the city and 450 miles highway with my 2AZ-FE on OME suspension and taller tires.
Things to look for if it's running rich: 1) How does the air filter look? 2) Is an injector stuck open? 3) Is the ECM commanding the injectors to run rich? (ECM error).
Things to be aware of if the engine is continually under load: 1) What size tires are you using? 2) What pressures do you run? 3) What aftermarket accessories have you installed?

I'm not the most knowledgable with the 1ZE-FE, so here's some documents you may find useful:
I might also start a thread discussing fuel additives, the chemical compositions, how often to use, where not to use, and the fact that non of them work as well as the manufacturers want you to believe.
 

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It certainly is running rich as evidenced by the black deposit where the exhaust leak was. What is causing it to run rich I have no clue and haven't been able to pinpoint it. I'm no mechanic, I've done all of the work with the help of my old man, but from the research I've done I reckon it could only really be the a/f ratio and 02 sensors causing a rich condition, possibly the cat as well?

To answer a few of your questions,
1) the air filter is in fair shape, definitely a little dirty but you can still see sunlight through it when held up. Gave it a few good smacks on the concrete along with a few gusts of compressed air.
2) I don't believe any of the injectors are stuck open, one of them was a tiny bit more loud that the other three, but cycled in the same manner. May be something to look into?
3) I wouldn't have the slightest clue how to check if the ECM is commanding the injectors to run rich. Is this something I can check with a bluetooth obd2 scanner? I was using torque lite to check fuel system loop status and clear any errant codes, but couldn't find a way to actually log any data, only real time info. I took a brief look at the fuel trim graphs, but again with no data logging it proved a fair bit dangerous/unruly to quickly glance at the graph on my phone while driving.

And to address the things to be aware of,
1a) Stock size Cooper Discovery with ~80% tread (P215/70R16)
2a) Recommended PSI of 29 all around
3a) No aftermarket accessories save a standard aftermarket deck & the factory roof rack

The mention of alignment may be something to check out as I'm unsure of when the alignment was last done on this vehicle. The previous owner seemed to at least try to take care of it with fairly thorough service records, but I never saw any record of an alignment. That being said, it doesn't pull to either side when my hands are off the wheel.

Thank you for the documents, I'm sure those will come in handy with troubleshooting.

I appreciate your response, you always have great information.
 

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Sounds like you and your Dad are making all the correct efforts (y)

On the fuel injectors: the one that sounds different from the rest, pull the associated spark plug and have a look. If it's wet . . . you found your problem. Four ways a fuel injector may fail: 1) fuel tank contamination prevents it from opening/closing fully 2) the ECM is erroneously commanding the injector to stay open too long 3) the injector itself not receiving commands from the ECM correctly 4) combustion side contaminates clogging the injector nozzle.

On the combustion side contaminates: It can be completely clogged causing a lean effect, or, it can be grossly clogged preventing the nozzle from atomizing fuel, causing a rich effect.

On the subject of fuel system cleaners, it's important to know they're best used at regular service intervals. Not singularly on randomized occasions. Think of them more like a vaccine, best used to maintain a healthy fuel system, not useful at all when a fuel system becomes hopelessly clogged.

OBDII information: the ST/LT fuel trims and EQ ratio (air:fuel) are what you want to look at. An EQ of 1.00 is supposed to be a perfect 14:1 stoichiometric ratio. Anything below 1.00 is rich, anything above is lean (counterintuitive to some).

Edit
I'm not as familiar with these 1AZ-FE documents, but Toyota also recognizes a loss of compression as being associated with poor fuel economy.
 

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OBDII information: the ST/LT fuel trims and EQ ratio (air:fuel) are what you want to look at. An EQ of 1.00 is supposed to be a perfect 14:1 stoichiometric ratio. Anything below 1.00 is rich, anything above is lean (counterintuitive to some).
In regard to the short term/long term fuel trims, what would be considered within tolerance? 0.95-1.05? Or should it always be exactly at 1?
And say it is off and running rich as I believe it to be, what might be the next step?
 

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Good questions (y)

The EQ will seldom be exactly 1.00, at least not for too long. It looks like on the 1AZ-FE the limitation is 0.62 - 1.38. Deviations between 0.9 - 1.1 aren't uncommon with heavy driving (2AZ-FE).
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Remember if the fuel injector or ECM has a software error, neither may report such and no DTC will be triggered. Refer to the "Testing Without Codes" document I shared above.
 

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03RavBC; did you clean your MAF sensor?
 

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03RavBC; did you clean your MAF sensor?
. . . cleaned the throttle body, maf sensor . . .
I'm not saying it can't cause a rich condition, but it my experience a dirty MAF sensor causes the engine to run lean and produce less power.

On a similar note, a malfunctioning MAF could erroneously send signals to the ECM commanding it to provide more fuel. This I see potentially could be caused by some kind of debris :unsure:
 

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@05RAV Thank you for all the info, I'm going to try to get a reading on the st/lt fuel trim sometime soon here. Maybe I'll try a different app.
Should the trim end up being off, it could be for any number of reasons, no? Likely culprit being the air fuel sensors upstream of the cat I suppose

@Commando Yes I did clean the maf, I didn't physically remove it from the intake hose but I did hit it with a fairly liberal spray of maf cleaner
 

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Should the trim end up being off, it could be for any number of reasons, no? Likely culprit being the air fuel sensors upstream of the cat I suppose
Correct, so long as everything on the intake side is functioning normally. Beings how you have no CEL, which would normally be the case for a chronic rich (or lean) condition, my money is on a malfunctioning fuel injector. But don't take my word for it, I've been proven wrong many times before . . .
. . . I didn't physically remove it from the intake hose but I did hit it with a fairly liberal spray of maf cleaner
I think what Commando is getting at is, there is no substitute for removing the sensor from the throttle body and giving it a good cleaning (y)
 

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''Newer'' Toyota are equipped with a permanent filter integrated to the filter housing (between the regular air filter and the MAF), that keeps the MAF always clean. Older Toyota's like our RAV4.2 don't have it, so the MAF often gets very dirty. When this happens; the engine is much less responsive and can even cause hesitation when flooring the gas pedal from a dead stop. From what I see, Toyota and Subaru seems to be the most sensible vehicles to dirty MAF. The best way to clean it correctly is to remove it from the air box.

This remark about the MAF was not directly related to your fuel economy problem, but just an add-on to your tune-up/maintenance task. A clogged air filter, bad fuel injector spray pattern, lazy/slow air/fuel sensor, worn spark plugs, offset coolant sensor, etc... they all affect the optimal fuel efficiency at different degrees.
 
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I’ll pop the air filter box off again later today and see if I can’t shimmy the MAF loose. If it is dirty, do you reckon it’ll be dirty as in bits of dirt that I can physically remove or will it be smaller bits that may be hard to see and thus need a good 360° spray of MAF cleaner to get rid of? Reason I ask is all I have at my place is brakleen and I don’t feel like driving across town to my dads today lol

I won’t have an opportunity to check the plug cylinders for a minute here but that’ll be the first thing on the list
 

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Ok so I've got the OBD2 logs finally. I thoroughly cleaned the MAF with sensor cleaner and blew some more dust out of the air box.
I'm not entirely sure what I'm looking at here, it'd be great if someone could take a quick glance at the file.
Might make my own thread here considering I basically just stole this other guys thread
For the file, I started the engine from cold, idled for a moment, drove down the street, idled to look something up, drove a bit, idled to look another thing up, drove and drove normally. gunned it a few times as well as you can see with the associated rpm’s
 

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If it is dirty, do you reckon it’ll be dirty as in bits of dirt that I can physically remove or will it be smaller bits that may be hard to see and thus need a good 360° spray of MAF cleaner to get rid of? Reason I ask is all I have at my place is brakleen and I don’t feel like driving across town to my dads today lol
If your air filter is doing its' job, it won't have visible particles of dirt at all. The sensor location is down stream of the EGR vent: The EGR slowly covers the sensor in a fog of fuel vapor, carrying nano-particles of dirt passed by the filter. After thousands of miles a grimy film develops over the sensor, inhibiting it from reading the air volume accurately. I love brake cleaner, but I wouldn't use it on the MAF sensor. I stick to the MAF sensor cleaners myself.

Nothing looks especially odd to me, it looks like the ECM is trying to function normally.
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These rich conditions are only 10-15% richer than I see under similar conditions. But, I do believe this is the problem with failing O2 sensors: they fail precisely because they stop providing the ECM correct data, and they only seem to fail to the rich side. So the data you see here can be skewed to appear normal, when it in fact isn't. Another way to detect this with telemetry is to use a standalone O2 detector.

Removing the spark plugs is also a good technique, not prone to erroneous processed data. Spark plugs don't lie. I mentioned checking the cylinder that had a different sounding injector, I should state for clarity it's important to look at all the spark plugs and compare them to each other. Don't bother just pulling one for a peek, look at ALL of them.
 

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. . . this is the problem with failing O2 sensors: they fail precisely because they stop providing the ECM correct data, and they only seem to fail to the rich side. So the data you see here can be skewed to appear normal, when it in fact isn't.
Let me demystify this statement:

An O2 sensor is measuring the delta of oxygen atoms between the exhaust gases and ambient air (hot and cold side of the O2 sensor). It does this by creating heat generated between two filaments inside the O2 sensor that produce a signal for the ECM.

Less O2 produces greater heat = rich condition, ECM schedules less fuel.
More O2 produces lesser heat = lean condition, ECM schedules more fuel.

There are two O2 sensors on my 2AZ-FE for example: the manifold sensor that actually detects O2 and helps the ECM manage EQ ratios, and the mid-pipe O2 that doesn't function to correct EQ at all, but monitors the health of the catalytic converter. Important to recognize it's the downstream sensor, behind the catalytic converter that triggers a DTC and illuminates the CEL. The O2 sensor in the manifold will never trigger a DTC on its' own, it will just continue to function worse and worse. Worse still, if you take it to Toyota they will just replace the O2 sensor that triggered the DTC, not the one worsening your fuel mileage. Understand from Toyota's perspective these are life long items that never need replaced.

Because the sensor is in the exhaust stream, it is prone to collecting combustion byproducts. Oil consumption, bad gas, dirty air filter etc. all cause the O2 sensor to send steadily worse information to the ECM. Now intuitively I would expect the O2 to fail to the lean side of EQ management. Why they fail to the rich side instead I can only hazard a guess? Maybe the contaminates are changing the density of the filaments thereby changing the ratio of oxygen atoms to temperature signal they produce? But the end result is a failing O2 sensor will tell the ECM it's at a 0.814 EQ when in fact it may be 0.60 :oops:
 

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Thanks for the write up, everything you said is clear to me and I appreciate it.
I’m curious about the standalone o2 probe you had mentioned earlier, I may look into that. In light of everything I’ve done to the car so far with few results, I reckon you’re onto something with the upstream o2/air fuel sensors. If I ever get this working as it should, I’ll post a follow up thread
 

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It is important to know the difference between O2 sensors (narrowband) and A/F sensors (wideband). Up to around the 2000 year, most cars came with conventionnal O2 sensors. It can see a rich or lean condition, but hardly tell at which point it is rich or lean. Now these O2 sensors are only used after cat (downstream). At around the 2000 year, most manufacturers switched to A/F sensors (wideband) for the upstream sensors. They can see with precision the actual air/fuel mixture (how much lean and how much rich the exhaust gases are). So it helped a lot to reduce fuel consumption and get lower emissions. These sensors are only accurate when they get to a certain temperature. When they are too cold; the ECU is in ''open loop''. This means it does not use the O2 or A/F signal to adjust the fuel trims. But these sensors are equipped with an heater to warms them more rapidly at a cold start. When the sensors are enough hot to get an accurate reading, the ECU stops the heater element and fall in ''closed loop''. At this moment the O2 or A/F sensors signals are used to adjust the fuel trims to the best air/fuel mixture possible.

Some manufacturers like Toyota decided that if there is an heater malfunction (open circuit or too high resistance), the ECU will never get in closed loop.... meaning that the engine will run richer than supposed!

Even if there is no check engine light, the sensors may get less accurate and slower reacting with aging and/or with contaminants build-up.
 
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With the 1AZ-Fe engine (2001-2003), two A/F sensors (upstream) are used. It is normal to see a reading difference between both when looking at the datas, because the bank1 and bank 2 are different sensors! They can't be interchanged. I don't understand why Toyota did this. But for 2004-2005 models (2AZ-FE), only one A/F sensor is used (upstream). Happily it's less expensive to change....
 
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It is important to know the difference between O2 sensors (narrowband) and A/F sensors (wideband).
I totally agree, but Toyota doesn't distinguish between the two. Neither in Toyota's parts catalogue or Technical Manuals are the wideband sensors called "A/F sensors". In Toyota's language the upstream and downstream sensors are both "O2 Sensors".
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But Commando is 100% correct, they can't be interchanged.
 
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