P0172 Running rich

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May 6, 2014
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hey all, got the obd light on yesterday when i got to work, turns out its code P0172, this the first time iv ever see this code in the 12 years iv had this car. (toyota celica gen7)
p0172.webp

cleared the code when i got to work and its not come back on.
so thought id get some checks done
checked this when i got home engine was warmed up by the time i got home coolant temp reading was 97c and rad fan was coming on at the time
my idle long term fuel trim seems to be cutting a lot of fuel
ltft1.webp


not sure if this is normal

when holding the revs at 2500rpm i get the below reading
ltftrev.webp


my o2 reading at idle is:
o2idle.webp


dunno if its faulty sensor the reading for sensor 1 just keeps bouncing up and down
and when revs held at 2500rpm i get:
o2rev.webp

his test was done when i got back home today from work, my work commute is 7.5 miles each way mostly highway. engine light came on yesterday when i parked up, hit redline on last stretch of road before entering work in 2nd and 3rd.
i usually redline it every day on last stretch to work and on last stretch when near home. although today i didnt hit the high revs at all.
here is my fuel record iv been keeping:
1760471115314.webp


only when going on long highway run do i get around 33mpg but not taken the car on a long run for a long time so just the 7.5 miles to work then 7.5 miles back home

is there an issue here or is this normal?
as its getting colder these days i think im gonna restrain from using high revs till the temp gauge is in the middle rather than when its in the 2nd notch up position.
to add, the car drives fine, no loss of power, no hesitation no odd noises, no odd smoke
 
The sensor 1 is doing its job, They cycle exactly like that. I second the leaky purge valve guess above. Block it/clamp the line and check your trims again.
 
Thanks for the replies, now I need to find out where the purge valve is on this car
Could this be caused by the way I fill up fuel in the car? When down to 3 bars left I fill up till it's totally full as in you can see the fuel at the top of the filler neck.
Can these purge valves be fixed with cleaning etc or is it replacement only?
 
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That is way too overfilled.

With any vehicle, fill until the first click from the pump, do not fill for a second click or beyond.
Dang iv been doing it for years when it clicks i carry on till it's at the top and can see it pool up
 
do done a couple of extra checks today when i got home
done maf flow tests at different revs
results below
maf800.webp

maf1500.webp

maf3000.webp


seems to be rising in linear fashion with the revs.
also calculated load i spotted at 82.5% when doing approx 4500rpm in 6th gear foot on the floor, too risky to keep an eye on the phone while its on the passenger seat so it may have gone higher at some point,
these readings seem indicate the MAF sensor to be in good working order. but im not a pro at this so will wait for you guys to respond.
i will get get a chance on the weekend to take a look at the purge valve thingy and if weather is good maybe take it off the car and run some carb cleaner or something through it?
 
Disconnect the evap hose (purge valve) and plug it so you don't have a vacuum leak into the intake. As the car is driven your total fuel trim (STFT + LTFT) will hopefully return to normal (within 10% of 0). If this is the case then the excess fuel is coming from a bad purge valve or evap canister. How long has it been since your last oil change?
 
Last oil change was around 5700 miles ago, it's due to be changed end of the month I change at 6k intervals
Disconnect the evap hose (purge valve) and plug it so you don't have a vacuum leak into the intake. As the car is driven your total fuel trim (STFT + LTFT) will hopefully return to normal (within 10% of 0). If this is the case then the excess fuel is coming from a bad purge valve or evap canister. How long has it been since your last oil change?
 
Possible to drain this canister?
It will evaporate all the liquid eventually if you just stop overfilling. This overfilling is likely the root cause of whatever failed and is causing the rich condition. Be sure to change the oil as well since it is undoubtedly fuel diluted and contributing some to the rich trims.
 
Understood, won't make the mistake of over filling it again.
Will change oil in 2 weeks time
 
Tested the purge valve today and it seems to be working fine, blowing through the pipe it's blocked, apply 12v and I can blow through it fine.

IMG_20251027_112140.webp


IMG_20251027_112131.webp
 
Car passed its MOT with no issue 2 days ago, flew through emissions test too so not sure what's going on.
I need to check fuel trims again, I did take it for a 120mile round trip yesterday and I'm keeping the tank below 3/4 from now on.
 
Did 400ish miles and no issue, filled up fuel tank and next day the P0172 code is back. I stopped filling when the pump clicked and didn't overfill but forgot that I should have filled it only 3/4 rather than full.
Could be leaking injectors, anyone know if that snake oil injector cleaner actually works or can injectors only be cleaned by removing and using ultrasonic bath?
Anyone recommend an injector cleaner?

Also engine oil was changed 2 weeks ago too
 
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To add, thermostat was also changed last weekend since temp gauge never gets to the mid mark unless it's idling for a long time, then as I start driving on highway temp needle drops back down a notch.
New thermostat has solved this and now it reaches mid mark on temp gauge very fast and doesn't drop down when driving. Should have changed this out 3 or 4 years ago but got lazy I guess since I didn't drive the car much in winter

IMG_20251116_114216.webp
 
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