Very interesting find dta1984! Just for curiosity sake, I just went out and dropped my glove compartment and pulled those same connectors. Mine are also covered in a light slightly brown oil. Some of my cables on the second connector down from the top also seem to have the oil on them as well..

Please keep me posted on your findings. Mine are not as covered as yours are (attaching photos below), but this may be the root of all the issues causing it to run lean/rich and burning up my o2/air fuel sensors and replacing them just masking the underlying issue here...

Attached Images

       

Come to think of it, The last time that i replaced my passenger A/F sensor, the connector did have an oily substance in it as well. I assumed it was dielectric grease that may have become hot and melted into more of a liquid, so i didn't put it back into the connection this time. I will have to pull that connector and see if it has this fluid in it again.

[QUOTE=BoostinZX;2832054]Very interesting find dta1984! Just for curiosity sake, I just went out and dropped my glove compartment and pulled those same connectors. Mine are also covered in a light slightly brown oil. Some of my cables on the second connector down from the top also seem to have the oil on them as well..

Please keep me posted on your findings. Mine are not as covered as yours are (attaching photos below), but this may be the root of all the issues causing it to run lean/rich and burning up my o2/air fuel sensors and replacing them just masking the underlying issue here...

Will do! You've definitely got a little oil in your connectors as well. I'd be curious how your downstream 02 connectors look. I remember one of mine was definitely covered in oil. For some reason didn't think nothing of it at the time....thought maybe it wasn't seated well.

Right as I was typing that haha. Interesting...

lol, definitely sounds like our issues are more related than I originally thought

I've had the P0174 MIL with VSC TRAC/Skid control off lights for about a month now. Had some other MIL codes which I fixed first per the FSM (replaced MAF meter), also cleaned the throttle body checked vent hose, intake manifold and air intake for leaks. Replaced gas cap. Haven't found any vacuum leaks and haven't detected any exhaust leaks yet. I'm in the process of checking all O2 sensors and so far they're good. One odd thing that stands out is even after replacing the MAF with a new one from Toyota I am getting a MAF reading of about 5 or 6 g/s at idle even after warmed up and FSM spec (have a 2007 FSM although my T4R is a 2005) says it should be more like 1.5 - 2.5 g/s. Anyone else seen this or know what might cause it to be sucking twice the air as normal? Wondering if that is what is causing my lean code. Also, not sure if it may be related but I have a belt squeak on start up that normally goes away after warming which I believe is from power steering pump pulley misalignment.

Not sure on the proper readings for the MAF, but maybe I need to look at that as well. I am still chasing the underlying issue of mine. I have cleaned my ECU and Air/Fuel Sensor connectors and i'm still throwing the codes and showing the Bank2 is dumping fuel via Torque Pro app for android.

Just another update. 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?

stumbled on this thread, while searching for clues, the MIl on my truck came on, p0174, my longterm fuel trims is reading 35%, shortterm is about 15%. meanwhile my longterm trims have been reading 18% for many years now, though no MIL, am wondering what changed.

am thinking of doing the airfuel sensor swap.
have you been able to resolve yours?

any closure on this?
ordered a fuel pressure kit and fuel cap from amazon, waiting to receive them, so i can cross out probable causes

Just a thought but if it's intermittent I wonder if dirt in the fuel tank is sloshing around and blocking the filter thing that is on the pump causing low pressure when driving?

Did you get the A/F sensors from Amazon or a Toyota dealer?

Just a quick follow up. I haven't been driving the car very much, but it hasn't messed up again for a while now. Fuel trims look good, etc. I still am not getting great gas mileage, but i'm assuming thats from the more aggressive tires.

To answer the question above, I have tried amazon denso sensors, rockauto denso sensors, and ordered direct from toyota, and all seemed to have the same result. This last set i'm on is rockauto.

I will keep updating this thread as I can to keep you guys in the loop of any changes. If anyone else has any possible solutions, definitely chime in for the people still having issues. I'm assuming at some point mine will come back, its probably just that since I don't drive it much anymore, its not had a chance to come back just yet.

update: i have driven about 30miles with over 6 restart cycles and the MIL is yet to illuminate,, scanning shows the LTFT2 has dropped to 28% from 36%, while LTFT1 has dropped to 12% from 18%, so still observing, have decided to disconnect the battery and get the ecm relearn , will see what happens after that

2nd update: false alarm, after unhooking the battery for 2hrs, reconnected and let it idle for 7mins, LTFT2 rose from 0 to 18%, drove for 2miles, and got a p0304 code- cylinder misfire, cleared it, and after 2 restart cycles, the dreaded&infamous p0174 reappeared again, so verdict is changing the bank 2 post CAT oxygen sensor didnt resolve the problem, as the LTFT2 is back at its usual 38% now

is your light still off?. bought denso sensors from amazon, replaced drivers side downstream sensor, still dumping fuel on bank 2, fuel trim solid at 38% and a p0430 code comes up on highway trips
what is the make of the sensor you bought off rockauto