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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 out 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 out 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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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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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?
. . . 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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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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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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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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I’m curious about the standalone o2 probe you had mentioned earlier, I may look into that.
Something like this:

Similar to a SMOG test, it's reading the actual concentration of gas (operator chooses the gas) the engine is producing. Laughably, in some States the City/County will plug into the OBDII port to determine this . . . which completely negates the purpose if the sensors are failing. You might remember the VW emissions scandal of 2015?
 

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Not even Toyota trusts the OBDII data for diagnosis:
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Notice the causes of a rich EQ in the bottom table: faulty MAF, faulty fuel injectors, plugged PCV, restricted air filter etc.
 

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CO/HC isn't measured by the car itself so it can't be read through the OBD.
Correct, the subject of this thread is about crappy mpg. The Toyota Technical Manual referenced above is detailing troubleshooting engine performance with no codes present, such as in the OPs case. The procedure explained by Toyota describes high CO/HC content when the engine is running rich, and likely sources of the problem.

If you have DTCs, obviously reading them via OBD would be very helpful (y)
 

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I thought maybe it was just some shitty gas(is that a possibility at all?) cuz I filled up at a new place that was just built, and for the next fill-up, I went to my go-to which is fuel depot(89 octane).
Crappy gas does impede fuel mileage, but to see as dramatic of decrease in mileage as you have, I would expect associated performance issues like knocking or rough idle to accompany. Your description of mileage loss sounds more nuanced, as happening over a greater period of time than a single tank of fuel.

The errant bump in mileage you saw after the tune-up can also be attributed to something put in the fuel, which is why I think the product used is suspect. If it were indeed a fuel system cleaner, there's no reason to believe immediately following treatment your system became so gummed up that it went back to it's original mileage.

I don't think a dirty fuel delivery system is the aggregate of your poor mileage.
 

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whoa, you know your stuff man. that's sick.
Not really.

I suggested a member had a serpentine belt problem . . . turned out to be worn main bearings.
I recommended a member not use a manual transmission ECM and he did anyway . . . worked fine enough evidently.
My batting average is not great :LOL:

Members in the 4.2 section are just trying to help, we figure things out together. My input isn't any better than the next member's. Worse even in some cases . . .
 

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They also recommended I do a fuel system service cuz there was probably a lot of carbon build-up or something. While they were doing the fuel service they were revving my car and stuff and soot were coming out the exhaust.
:oops:

Your engine is absolutely developing fuel and combustion byproduct contaminates as years go by, and I do believe regular fuel system cleaner is important to maintaining optimum performance. But no fuel additive I know of does the job in a single tank of gas, and as dirty as yours sounds, it may take several.

On fuel system cleaners: They are maximumly beneficial if you can use the entire bottle in one tank non-stop, like a road trip for example. Which sounds like you did (y)

But understand what detergents giveth, they taketh away. All the contaminates they remove go somewhere, and that somewhere is out the exhaust. All of this passes by the wide band O2 sensor or A/F sensor Commando and I have been talking about. Its' exposed to all of these contaminates before they are mostly burnt up in the catalytic converter. And if you've been following along, it's precisely this sensor that helps the ECM manage fuel delivery.

On a vehicle with 166k miles, it no doubt is a combination of things that are worsening your fuel mileage. Follow 03RavBC's troubleshooting and you'll see he's covering all the bases. Your RAV would benefit from the same, because I don't believe a fuel treatment alone is going to solve your problem.
 

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This is progress :D

If the sensors were largely causal to the poor fuel mileage, I'd expect to see a noticeable improvement right away. I think you've narrowed your search down to the fuel injectors. Pull those spark plugs and take a photo for us (y)
 

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For starters, great photos (y) They answer a lot of questions.

I think they look pretty good actually 🤷‍♂️ Not what I expected to see for sure. Is that because they're new? Maybe? But even fresh plugs will show telltale signs of lean/rich mixtures after a short duration.

A couple questions further:
1) Do you by any chance have the original plugs?
1a) If NO, do you remember how they looked in comparison to these?
2) Did changing the plugs have any effect on fuel mileage?

If the original plugs were indeed getting dangerously close to carbon fouling, I'd expect at least a temporary improvement in fuel mileage with new plugs, beginning to worsen again shortly after.

Let me just break down my decision matrix:
✔ The OBDII data looks good, ECM looks like it's managing EQ's correctly
✔ New O2/AF sensors should be providing correct data
✔ You've cleaned the MAF
✔ New spark plugs, iridium (y)
✔ Plugs don't appear to be operating in exceedingly rich conditions to me, backing up ECM data
✔ No DTCs

All of this really makes a difficult case to explain fuel management problems. The problem I'm having wrapping my head around is the extent of your "Crappy mpg???". I agree with you, you're getting absolutely terrible milage :oops: I can't completely rest the case against a faulty injector(s), but the downstream data just doesn't warrant it IMO.

Hear me out, I've never had this problem myself but I've known others who have: how does your fuel system look from the filler neck to the engine? Are you leaking/spilling fuel out as you drive? I imagine you would know if fuel was dripping while parked, but can you detect any evidence of leaks while you're driving? These older RAVs are susceptible to corrosion of fuel system components.
 

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What’s odd about the new plugs being clean is that I know the vehicle is running rich. At least I did before I plugged the exhaust leak a month ago. The area where the hole was was completely black with soot. Changes I’ve made and parts I’ve swapped since then may have effected just how rich it runs, but I can say with certainty that it was running very rich recently. The proper end of the exhaust is still black now but I haven’t gone and cleaned it to compare if it gets black again . . . As for the downstream data, I know with almost complete certainty that the catalytic converter is toast, so is it not possible that the downstream sensors are simply reading the wrong data?
This is really good information (y)
It explains that your RAV doesn't have a fuel management problem, it has a problem producing power at all. A failed/failing catalytic converter will cause the engine to work harder to produce power - a greater percentage of power is required at all times. The increased fuel flow in combination with the poorly functioning catalytic converter produces a large amount of "soot" in the exhaust. You may also see a black cloud from the exhaust under certain throttle settings. An OBD reader can detect this under the calculated load column, but it's of little good without knowing the "before" value. It works great for testing mods though . . .

I went ahead and ordered 4 remanufactured injectors from rockauto and they should be here shortly . . . It’s only $150 anyway.
I think you're smart for doing this, I was avoiding recommending to you spending money I wasn't convinced would yield a benefit.
I haven’t noticed any fuel leaking nor a smell of gas anywhere around the car. I reckon if there’s a hole in the filler neck I’d likely be able to smell at least a faint smell of gas, no?
Correct, it was a shot in the dark. Now that you mentioned you have a bad catalytic converter it makes a lot of sense. I think that's your problem (y) I've personally dealt with this very issue on past vehicles, although none were Toyotas.

Don't sell your RAV just yet, replace that manifold ;)
 

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You figure a bad cat can have that big of an impact of fuel economy?
Like an axe murderer will a bad cat kill your fuel economy. Your engine will perform like it's pulling a heavy load . . . all the time. And so it goes for systems that degrade slowly over time, the operator detects something has gone wrong about as well as your brain detecting its' oxygen deficient.

The last engine I dealt with this was a 3.0L Duratec. I spent thousands of dollars chasing secondary and tertiary problems. Nothing helped whatsoever. Finally the problem escalated so badly the engine could hardly pull the SUV up a mountain pass, did Ford reluctantly replace the cats like I asked many times before. Problem solved 😑

This time, and the time before, started as ever worsening fuel milage that I couldn't resolve otherwise.

This is one repair I’m not looking forward to footing the bill for haha
On order magnitude cheaper than replacing the whole vehicle ;) Used RAV4.2s are going for >$10,000 in the U.S.
I’d likely be well served to get a smog test done similar to the device you posted earlier in this thread. Might tell me with 100% certainty that the cat has actually gone bad before I spend ~$600
I agree (y)
 
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