BoostinZX
New member
I'm hoping someone here can shine some light on some issues my wife's '05 V8 T4R is experiencing.
About 8 months ago, it started throwing codes and smelling very strong through the exhaust. (I can't remember what the codes were now, but pretty sure it was P0171 and P0173 possibly) but it led me to changing the upstream O2 sensors, gas tank cap, as well as the MAF sensor.. The gas tank cap didn't change anything, MAF didn't seem to help, but once i changed the upstream o2 sensors, it seemed to help. We drove it for a while like this and the exhaust smell was not nearly as strong. Then about 3 months ago when we got the vacuum cleaner sound under the hood during cold startup (secondary air injection system failure). I purchased the bypass kit (without plates) from slyfox here on the forum and installed it, and it bypassed the system. I was getting error codes that said stuck closed, so thought i was in the clear. Car seemed to run great until the past 2 weeks. Now we have the following.
P0174 Code (keeps coming back after resetting it)
Rough Idle (like an intermittent miss). Especially bad when in gear at a stoplight
Hesitation when you accelerate with slight throttle
Very strong gas/un-burnt fuel like odor from the exhaust, not rotten egg smell.
The car runs perfect (or seems to when under full throttle). Also seems to run fine or much better until the car gets up to temperature.
I checked for vacuum leaks by spraying carb cleaner around all the vacuum lines i could find, cleaned throttle body, ran fuel system cleaner through it a few times, checked the spark plugs (they look normal), switched to 100% premium gas and nothing has helped.
EDIT:
I have also added the secondary air injection bypass plates to try and see if they may have been slightly stuck "open" and thought that would 100% isolate it being that system from being the culprit, and the issue still remains. After installing the plates, we drove the car for about 5 miles and it ran perfectly, then right as we got home it started doing it again.
Update: 7/21/16
I rented a fuel pressure tester today. Car holds a steady 42psi of fuel pressure, even when the engine starts running rough after it warms up and throws the p0174 code. I let it idle and ran it up and down to 2500rpms a few times and no change... so Fuel Pressure looks good.. It also held good pressure for up to 10-15 minutes after I turned the car off. It only ever dropped down to 40psi... So I guess I can rule out the fuel pump and pressure regulator/etc..
Any ideas? I have read through a bunch of threads and some think it could be injector or fuel pump related. Has anyone had a similar issue or any suggestion on where to look next? Any help is greatly appreciated!
Update: 8/11/16
I figured out the problem. It was a faulty Upstream A/F Sensor that I had replaced a year ago. I swapped the sensors from side to side and the problem swapped sides. Replaced the sensor and all is good now. Hope this thread helps someone else out!
Update: 9/22/17
The car is still experiencing the same issues. It seems as though replacing the front A/F Sensors were just masking a larger problem that I have yet to trace down. I will keep you posted on any discoveries I make. Right now, i'm leaning toward an intermittently failing injector since the problem is hit/miss... runs fine for a while, then goes back into running rough/throwing codes/smelling like raw fuel.. then back to normal...
Update: 11/3/17
May have discovered another rabbit hole to go down with this issue. A fellow member here with similar has discovered that there is an issue with ATF fluid making its way up the cabling from the ATF sensor and up into the ECU and down into the A/F and O2 Sensor connectors. Out of curiosity, I took the glove compartment off and checked my main ECU connectors, and sure enough the 2nd one down and all 3 blow it have a fluid on them. Its not much, but is definitely not supposed to be there. I have yet to investigate my A/F sensor connectors, but the last time that I swapped them out, i do remember noticing the passenger side one was full of a brownish fluid. At the time i assumed it was just the dielectric grease i put in there got hot... but its clearly a different issue altogether. You can follow his thread here: oil wicking up my o2 sensor wire harness? - Toyota 4Runner Forum - Largest 4Runner Forum
Update: 10/23/18
Just another update. Light came on a few months ago again and the exhaust smell returned as well. Checked with the torque pro app and i'm "lean bank 2" again so its dumping fuel again... Cleaned all connectors even on the o2 sensors and cleared codes multiple times... code finally stayed off for a bit, but watching my fuel trims i'm still dumping fuel on bank 2... Something has to be causing my o2 sensors to slowly fail... i definitely have oil in my ecu and connectors but not much at all... i'm thinking it has to be a secondary issue at this point and that there is something causing my o2 sensors to go bad overtime on that bank for whatever reason... any ideas?
Update: 6/15/21
It has been doing this off and on for the last few years still. I hardly drive the car unless I need to haul my bikes somewhere so it sits most of the time now. Sometimes it will run fine, and sometimes it will run and be pulling tons of fuel (per torque pro app). Still no resolution on what the problem is, just wanted to give everyone an update and see if anyone else had figured out a possible solution. I am now throwing a P0172 & P0175 code pretty consistently.
I will keep updating this thread as well with any other discoveries that we make... hoping this helps someone else out in the future. Seems like a very very strange issue.
About 8 months ago, it started throwing codes and smelling very strong through the exhaust. (I can't remember what the codes were now, but pretty sure it was P0171 and P0173 possibly) but it led me to changing the upstream O2 sensors, gas tank cap, as well as the MAF sensor.. The gas tank cap didn't change anything, MAF didn't seem to help, but once i changed the upstream o2 sensors, it seemed to help. We drove it for a while like this and the exhaust smell was not nearly as strong. Then about 3 months ago when we got the vacuum cleaner sound under the hood during cold startup (secondary air injection system failure). I purchased the bypass kit (without plates) from slyfox here on the forum and installed it, and it bypassed the system. I was getting error codes that said stuck closed, so thought i was in the clear. Car seemed to run great until the past 2 weeks. Now we have the following.
P0174 Code (keeps coming back after resetting it)
Rough Idle (like an intermittent miss). Especially bad when in gear at a stoplight
Hesitation when you accelerate with slight throttle
Very strong gas/un-burnt fuel like odor from the exhaust, not rotten egg smell.
The car runs perfect (or seems to when under full throttle). Also seems to run fine or much better until the car gets up to temperature.
I checked for vacuum leaks by spraying carb cleaner around all the vacuum lines i could find, cleaned throttle body, ran fuel system cleaner through it a few times, checked the spark plugs (they look normal), switched to 100% premium gas and nothing has helped.
EDIT:
I have also added the secondary air injection bypass plates to try and see if they may have been slightly stuck "open" and thought that would 100% isolate it being that system from being the culprit, and the issue still remains. After installing the plates, we drove the car for about 5 miles and it ran perfectly, then right as we got home it started doing it again.
Update: 7/21/16
I rented a fuel pressure tester today. Car holds a steady 42psi of fuel pressure, even when the engine starts running rough after it warms up and throws the p0174 code. I let it idle and ran it up and down to 2500rpms a few times and no change... so Fuel Pressure looks good.. It also held good pressure for up to 10-15 minutes after I turned the car off. It only ever dropped down to 40psi... So I guess I can rule out the fuel pump and pressure regulator/etc..
Any ideas? I have read through a bunch of threads and some think it could be injector or fuel pump related. Has anyone had a similar issue or any suggestion on where to look next? Any help is greatly appreciated!
Update: 8/11/16
I figured out the problem. It was a faulty Upstream A/F Sensor that I had replaced a year ago. I swapped the sensors from side to side and the problem swapped sides. Replaced the sensor and all is good now. Hope this thread helps someone else out!
Update: 9/22/17
The car is still experiencing the same issues. It seems as though replacing the front A/F Sensors were just masking a larger problem that I have yet to trace down. I will keep you posted on any discoveries I make. Right now, i'm leaning toward an intermittently failing injector since the problem is hit/miss... runs fine for a while, then goes back into running rough/throwing codes/smelling like raw fuel.. then back to normal...
Update: 11/3/17
May have discovered another rabbit hole to go down with this issue. A fellow member here with similar has discovered that there is an issue with ATF fluid making its way up the cabling from the ATF sensor and up into the ECU and down into the A/F and O2 Sensor connectors. Out of curiosity, I took the glove compartment off and checked my main ECU connectors, and sure enough the 2nd one down and all 3 blow it have a fluid on them. Its not much, but is definitely not supposed to be there. I have yet to investigate my A/F sensor connectors, but the last time that I swapped them out, i do remember noticing the passenger side one was full of a brownish fluid. At the time i assumed it was just the dielectric grease i put in there got hot... but its clearly a different issue altogether. You can follow his thread here: oil wicking up my o2 sensor wire harness? - Toyota 4Runner Forum - Largest 4Runner Forum
Update: 10/23/18
Just another update. Light came on a few months ago again and the exhaust smell returned as well. Checked with the torque pro app and i'm "lean bank 2" again so its dumping fuel again... Cleaned all connectors even on the o2 sensors and cleared codes multiple times... code finally stayed off for a bit, but watching my fuel trims i'm still dumping fuel on bank 2... Something has to be causing my o2 sensors to slowly fail... i definitely have oil in my ecu and connectors but not much at all... i'm thinking it has to be a secondary issue at this point and that there is something causing my o2 sensors to go bad overtime on that bank for whatever reason... any ideas?
Update: 6/15/21
It has been doing this off and on for the last few years still. I hardly drive the car unless I need to haul my bikes somewhere so it sits most of the time now. Sometimes it will run fine, and sometimes it will run and be pulling tons of fuel (per torque pro app). Still no resolution on what the problem is, just wanted to give everyone an update and see if anyone else had figured out a possible solution. I am now throwing a P0172 & P0175 code pretty consistently.
I will keep updating this thread as well with any other discoveries that we make... hoping this helps someone else out in the future. Seems like a very very strange issue.
Last edited:
... going to try something i should have tried a while ago, swapping the front A/F Sensors to see if the code changes banks.. long shot but worth a shot i guess to see if i have a faulty sensor...
