Don't mean to thread jack but I was trying to find an answer without posting. I did get the P0171 code previously but after cleaning the MAF sensor it went away. Changed the O2 sensors, Fuel filter, Coils and sparks too. I still get a random hesitation and misfire with little power. Have to pull over and re-start the car but no code. Suggestions?
P0171 code
- Thread starter Bt08231
- Start date
shaneclark562
New member
Has anyone replaced the upstream O2 or called the fuel/air sensor while trouble shooting this issue? I am trying to do it however the plug sits on top of the transmission and I cannot figure out how to get the darned thing out without dropping the trans or lifting it off the frame.
Manual 4wd 2000 runner.
Sent from my SM-G950U using Tapatalk
Manual 4wd 2000 runner.
Sent from my SM-G950U using Tapatalk
TheDurk
Elite Member
Actually, I had a P0171 that I was able to resolve by swapping the A/F sensor, even though a self-described "Toyota Master Tech" on here told me it could not be the cause. The FSM does list it as a cause:
I have the same rig ('99 and '00 are clones) and I think I got that clip undone through the shifter hole. I then left it unattached without further problems. Then you can just unbolt the sensor, throw it over the top, and undo the connection where it hangs down on the other side.
Last edited:
RS Dude
Member
I just resolved my p0171 code that popped up the other day. I spent $9 on some CRC Maf sensor cleaner and about 15 minutes and that cleared the check eng light and error code. It also ended my bad pinging (worse as the temps rise). Will be replacing ign wires with NGK, new plugs, new denso O2 sensors, and new oem pcv valve.
I'm getting this code as well. I believe it started when I replaced my valve cover gaskets. I cleaned the throttle body and IAC valve. I WAS getting a high idle as well.
Things I've Checked/Replaced:
-checked the TB gaskets.
-replaced MAF
-replaced both O2 sensors
-replaced the charcoal canister thing (forget what it's called)
-replaced a torn air boot
-checked the vacuum lines & replaced a few
-replaced throttle position sensor
-replaced fuel filter
After replacing the Throttle Position Sensor, my high idle is no longer an issue. However, the code was triggered AGAIN today!
I think it's one of 4 culprits: 1) over cleaning the throttle body and somehow it's not closing all the way anymore or 2) idle air control valve is shot or 3) the charcoal canister i bought via ebay is bad or 4) bad fuel injectors (242k miles on original).
I have seen decreased MPG and I'm getting a stronger smell of gas outside the vehicle.
I have purchased reconditioned fuel injectors (MotorWest Performance; recommended by Timmy). Bought a used IAC valve fr ebay. Guess I'll start here.
Any input?
Things I've Checked/Replaced:
-checked the TB gaskets.
-replaced MAF
-replaced both O2 sensors
-replaced the charcoal canister thing (forget what it's called)
-replaced a torn air boot
-checked the vacuum lines & replaced a few
-replaced throttle position sensor
-replaced fuel filter
After replacing the Throttle Position Sensor, my high idle is no longer an issue. However, the code was triggered AGAIN today!
I think it's one of 4 culprits: 1) over cleaning the throttle body and somehow it's not closing all the way anymore or 2) idle air control valve is shot or 3) the charcoal canister i bought via ebay is bad or 4) bad fuel injectors (242k miles on original).
I have seen decreased MPG and I'm getting a stronger smell of gas outside the vehicle.
I have purchased reconditioned fuel injectors (MotorWest Performance; recommended by Timmy). Bought a used IAC valve fr ebay. Guess I'll start here.
Any input?
gamefreakgc
Elite Member
I can provide a bit of diagnosis and thoughts on your list of culprits. A P0171 can be grouped into two large culprits, a sensor pertaining to fuel or air delivery to the engine (uncommon) or a leak in the air system causing unmetered air to enter the engine (most common).
1) Over cleaning the throttle body usually results in a clogged IAC valve when deposits slip through the holes on the bottom of the throttle body which would result in high idling, poor idle when hot on a long drive, or intermittent stalling. I've yet to hear of one throwing a P0171 code.
2) See answer 1 above.
3) The charcoal canister would not throw a lean code unless the vacuum lines themselves are leaking air, or the unit was somehow cracked or compromised. A clogged charcoal canister will normally throw EVAP codes. I would say this is unlikely.
4) Bad fuel injectors, or my top suggestion of bad fuel injector o-rings could be the culprit. Trust your nose, if you are smelling unburnt fuel, that means there's a leak downstream of the injectors. Fuel smell is never a normal thing and should be addressed immediately. A bad o-ring on the fuel rail or injectors themselves can also cause un-metered air to enter the engine and throw a code. If you are smelling a combination of un-burnt fuel AND a sulfur like smell, it's and exhaust leak between the cylinder heads and the first catalytic converter, I just took care of that on my 4Runner.
Devbot
New member
Sounds like you IAC is the only thing, I'd give it a shot. Mine was like $50 (off amazon iirc, was OEM) and took me maybe 30-40 minutes all said and done. Just don't forget the gasket.
Unless you have an 01-02. One of the small changes to the engine bay was making the throttle body and IAC integrated as one unit, and they're MUCH more expensive too replace. You could clean it, but personally I figured why not replace it if it's so cheap and at such high miles? Gonna need to be done eventually, and if it's lasted 200k so far ~~
Unless you have an 01-02. One of the small changes to the engine bay was making the throttle body and IAC integrated as one unit, and they're MUCH more expensive too replace. You could clean it, but personally I figured why not replace it if it's so cheap and at such high miles? Gonna need to be done eventually, and if it's lasted 200k so far ~~
Well, some new pieces to the puzzle. (242,000 mi)
I tried pulling on the throttle linkage a few minutes after starting the truck. The idle immediately returned to around 700RPM. I think this is the source of my high idle. Extra air is getting into the engine because the butterfly valve is closing/seating correctly. I saw a thread about adding a thin washer w/ a 3/8" hole. I'm going to do this mod. BTW, my MAF was running above 5g/sec at idle and the second I pulled on the linkage, the idle dropped and the MAF returned to the correct range of 3.3-4.7g/sec. So I'm going to give this mod a go tomorrow.
Unfortunately, I'm now experiencing major losses of power when driving. Very odd. First the problem presented itself as a delayed response when I'd step hard on the gas peddle last week. Today, I cleaned my MAF (replaced 1'18) and added seafoam to the gas at the highest recommended concentration 2oz/gal. Took it for a drive and within about 15min, pressing on the gas peddle was having no effect on RPM or acceleration. At slow speeds, as the engine attempted to respond to the gas pedal, the truck lurched at times and then eventually stalled. It would start right up. No issues starting. Happened a bunch of times as I attempted to get home. I added more gas for fear I added too much sea foam and am letting it idle in the garage for a bit. I found at times, keeping the RPM high, helped while driving down the road.
My guess is a fuel delivery problem: fuel pump or injectors. What's your best guess?
Appreciate the insights!
I tried pulling on the throttle linkage a few minutes after starting the truck. The idle immediately returned to around 700RPM. I think this is the source of my high idle. Extra air is getting into the engine because the butterfly valve is closing/seating correctly. I saw a thread about adding a thin washer w/ a 3/8" hole. I'm going to do this mod. BTW, my MAF was running above 5g/sec at idle and the second I pulled on the linkage, the idle dropped and the MAF returned to the correct range of 3.3-4.7g/sec. So I'm going to give this mod a go tomorrow.
Unfortunately, I'm now experiencing major losses of power when driving. Very odd. First the problem presented itself as a delayed response when I'd step hard on the gas peddle last week. Today, I cleaned my MAF (replaced 1'18) and added seafoam to the gas at the highest recommended concentration 2oz/gal. Took it for a drive and within about 15min, pressing on the gas peddle was having no effect on RPM or acceleration. At slow speeds, as the engine attempted to respond to the gas pedal, the truck lurched at times and then eventually stalled. It would start right up. No issues starting. Happened a bunch of times as I attempted to get home. I added more gas for fear I added too much sea foam and am letting it idle in the garage for a bit. I found at times, keeping the RPM high, helped while driving down the road.
My guess is a fuel delivery problem: fuel pump or injectors. What's your best guess?
Appreciate the insights!
Last edited:
Devbot
New member
Sometimes when your vehicle has too lean of a mix the ECU will retard your ignition timing to prevent damage and as such you'll lose loads of power (this is what "limp mode" is and is very often triggered during P0171. However, it's usually only present with a CEL if I'm not mistaken). Does it keep coming back or is this now happening with a clear dash?
A decent way to check your injectors is to grab a long screwdriver or socket extension, and put your ear on one end and the other on the injector. They should all sound relatively the same, a slight variance can be attributed to age/wear but anything real noticeable is obviously a red flag. If your fuel pump was going out, a different code is almost always thrown (P0080 or something). If it was fuel related my first guess would be the filter but it sounds like you've pinpointed it to the throttle - however I wouldn't be surprised if you maybe weakened some old varnish in the filter and made it's way to the injectors, from the Seafoam.
Personally I think Seafoam is pretty weak. I recommend either RedLine SI-1 or the new BG44k Platinum. Both are terrifically strong, and I practically attribute them to having valves cleaner than my dinner plate at almost 300k. Seafoam itself is nothing but isopropyl alcohol and naphtha suspended in pale oil. I'd recommend trying the TB mod, and if that doesn't fix it then change out your fuel filter and throw in some of the aforementioned cleaners. (I never do just one treatment, usually 2-3 tanks for good measure). Start cheapest and work big.
Edit: How do your spark-o-lators look? I assume they're probably fine but it's another cheap place to start. Mine were practically lacking an electrode and still zapping good enough to run
A decent way to check your injectors is to grab a long screwdriver or socket extension, and put your ear on one end and the other on the injector. They should all sound relatively the same, a slight variance can be attributed to age/wear but anything real noticeable is obviously a red flag. If your fuel pump was going out, a different code is almost always thrown (P0080 or something). If it was fuel related my first guess would be the filter but it sounds like you've pinpointed it to the throttle - however I wouldn't be surprised if you maybe weakened some old varnish in the filter and made it's way to the injectors, from the Seafoam.
Personally I think Seafoam is pretty weak. I recommend either RedLine SI-1 or the new BG44k Platinum. Both are terrifically strong, and I practically attribute them to having valves cleaner than my dinner plate at almost 300k. Seafoam itself is nothing but isopropyl alcohol and naphtha suspended in pale oil. I'd recommend trying the TB mod, and if that doesn't fix it then change out your fuel filter and throw in some of the aforementioned cleaners. (I never do just one treatment, usually 2-3 tanks for good measure). Start cheapest and work big.
Edit: How do your spark-o-lators look? I assume they're probably fine but it's another cheap place to start. Mine were practically lacking an electrode and still zapping good enough to run
Last edited:
Just replaced the fuel filter (OEM) in May. I already have the injectors so I'm going to put them in. The goal is to get the high idle and this new problem resolved so that I can put a supercharger on (as long as compression is good). But don't dare attempt the supercharger project until i get these problems resolved once and for all.
I had the P0170 CEL today and cleared it before I took the truck for a drive. Throughout today's acceleration/lurching issue, the CEL remained off. It's still off as the truck idles in the garage.
Appreciate the fuel additive insights. Wasn't aware!
Update. Replaced fuel injectors and installed the new throttle body. truck drives like new. The low idle issue is gone. But I don't think this was what was causing the sudden engine dying. Turns out I had two electrical issues. The ppsitive battery terminal was shot and the alternator was bad. What little charge the battery was getting was quickly consumed and as sokn as the battery voltage dropped, the truck exhibited the previous problems (lurching/engine died). Replaced the battery, started the truck and disconnected the battery. the truck instantly died.
have the cs144 and the adapter plug. installing this week. psyched to get these issues behind me!
now, one last issue. I'm still smelling gas. not as strong now. I'm going to replace the spark plugs with the ones id use w a supercharger as I prepare for that.
so 3 potential things to check I guess: catalytic converter, headers/manifold or charcoal canister? anything else I should check?
how does one know if the charcoal canister is working? could that throw a p0170?
I have zero rust. no leaking fuel. engine is running great. idles perfectly. both o2 sensors new. the ecu was reset. I'm pretty stumped.
have the cs144 and the adapter plug. installing this week. psyched to get these issues behind me!
now, one last issue. I'm still smelling gas. not as strong now. I'm going to replace the spark plugs with the ones id use w a supercharger as I prepare for that.
so 3 potential things to check I guess: catalytic converter, headers/manifold or charcoal canister? anything else I should check?
how does one know if the charcoal canister is working? could that throw a p0170?
I have zero rust. no leaking fuel. engine is running great. idles perfectly. both o2 sensors new. the ecu was reset. I'm pretty stumped.
19963.4lsr5
New member
Usually if there is a problem with the EVAP system you’ll get a leak code (small or large) or the readiness monitor won’t set.
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
Devbot
New member
Do you smell any sulfur? If you have an exhaust leak (before or at the cat) it should smell of both gas AND rotten eggs. If you don't, and your fuel rails look alright, I would look into the charcoal canister, as fuel odor and poor performance are both big signs of one failing. Do you notice a drop in MPGs?
In case you haven't already, sniff around he canister while running. Probably will be impossible with the all the wind stirred up by the fan but worth a try. If you don't have any codes thrown or pending codes related to the charcoal canister itself, I would assume it's probably a bad purge valve that isn't functioning properly when told to. I believe the proper way to test charcoal canisters is with a vacuum pump/gauge but I'm not totally sure. Just my 2 cents
In case you haven't already, sniff around he canister while running. Probably will be impossible with the all the wind stirred up by the fan but worth a try. If you don't have any codes thrown or pending codes related to the charcoal canister itself, I would assume it's probably a bad purge valve that isn't functioning properly when told to. I believe the proper way to test charcoal canisters is with a vacuum pump/gauge but I'm not totally sure. Just my 2 cents
yes, I've had a drop in mpg's. I was attributing it to the e-rated ko2's. hmmm.
no sulfur smell at all. is the purge valve part of the charcoal canister?
jgue467
Senior Member
P0455 relates to charcoal canister issues.
checked my notes. the purge valve was replaced in '18. is there a way to test it?
