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Discussion Starter · #1 · (Edited)
2005 Toyota Rav4
2.4 L
Automatic
182k miles

Bought the car at 55k miles. Used to get great fuel economy, but it's been poor for several years. Last two tanks have been 20 and 21mpg. Mixed city highway driving.
I've been playing with a simply OBD II scanner. Here's what I understand.
The long term fuel trims are high indicating a lean condition

Notable maintenance:
  • New denso plugs and coils around 160k miles
  • Cleaned MAF sensor and Throttle body last week, though I did not remove the TB for a proper cleaning, but I did at 150k miles. Not sure if I've ever cleaned IACV properly.
  • Ran Seafoam in gas tank two tanks ago
  • Very regular oil changes, burns no oil
  • Original Cats
Symptoms:
  • I've seen Long term fuel trims as high at 25% while cruising at 40 MPH, but is usually around 15%. Short Term always seems pretty low.
  • I noticed that under WOT the Throttle position only read 80% open and load only at like 66%. I was going about 15mpg when and then floored it.
  • Poor fuel economy
  • Also, I still occasionally encounter the low speed surge in stop and go traffic.
  • Very smooth idle otherwise
  • No check engine lights or codes

I have data at Idle and 2500 RPM, and a Wide open throttle road test below

WOT: 2005 Rav4 OBII scanner WOT

Any ideas what I should be testing to trying next?

IDLE

Finger Gadget Communication Device Material property Gas
Communication Device Gadget Audio equipment Gas Machine

IDLE O2B1S1 and S2 (V) Graphs:
Gadget Finger Mode of transport Air travel Gas


Automotive tire Vehicle Gadget Mode of transport Finger


2500 RPM
Vehicle Gadget Automotive tire Finger Communication Device
Watch Automotive tire Vehicle Communication Device Audio equipment

2500 RPM O2B1S1 and S2 (v) Graphs
Finger Gadget Audio equipment Display device Electronic device
Cloud Light Gadget Finger Vehicle
 

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Discussion Starter · #3 ·
Thanks for the feedback! I don't have the equipment to do that, but have a good shop if I end up going that route. Given that info though, I may try to run some more fuel cleaner...
 

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Discussion Starter · #5 ·
Just an update - I was grabbing some Redline at the auto parts store and thought it would prudent to check my battery and alternator. They said the voltage regulator was bad, so I'll be addressing that next to see if that helps!

Also, I noticed that in WOT it goes to Open Loop, which is probably why the fuel trims drop back down. Under any acceleration, long term fuel trim maxes out to 25%.
 

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Discussion Starter · #7 ·
Hey Phil, would you mind reviewing my voltage outputs before I replace the Alternator? Just want to make sure it's bad before I replace it...
My multimeter would only go to 12V for a "Battery Test"

Battery output, vehicle off: 12.5 volts
Turned car on: 13.5 volts at first. After a few minutes it was 12.5 steady.
I followed a guide to test for a leaking diode. Changed to AC, connected to negative battery terminal and alternator output. Car running: .450 volts to .550 volts. Always changing.
 

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Discussion Starter · #9 ·
Thank you! I'm taking it to my shop tomorrow. I'm stepping too far out of my basic mechanical knowledge...
I spoke with the mechanic and he asked me what symptoms I was having with the alternator and I explained all the long term fuel trims. He was pretty surprised lol. Agreed it's usually fuel delivery but said you definitely have to get the electronics right before moving on to anything else. :)
That's the thing, it's been super reliable so I'm a bit skeptical it's the alternator. But who knows, I have no idea if a different shop used OEM when it was replaced like 6 years ago.
 

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Discussion Starter · #11 ·
Looks like I'm in the market for a new battery. Shop says that it's weak. Alternator testing fine.
They drove it and did a smoke test for vacuum leaks, didn't find anything else wrong with it.
They also didn't even charge me. Maybe because I toldt the shop owner that he left his headlights on :)

I'll report back after more testing...
 

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Discussion Starter · #12 ·
Update: I'm no longer seeing any 25% LTFT's!

2500 RPM LTFT's have improved as well from 15% previously to 5.5% LTFT (plus 3.9 STFT).

But, I'm still seeing the same 15% LTFT while accelerating or under load. ECU is clearly still recalibrating though. And fuel cleaner still working its way through. I'll post a real update after a tank or two of gas.
 
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