FRONT O2 SENSOR FUFUFU

Note: I've had my battery cable off a ton of times for various reasons, and probably 20 times in the last 3 months. It has run crappy before, and crappy after... until a little over an hour ago - so I do not think this can be attributed to the ECU being reset at all.

Figured I may as well install the new Denso o2 sensor I had purchased now that I broke the stuck bolt off on the upstream one. Put on a jacket and a head lamp and did it in like 3 minutes outside. Cleaned up the threads, found two compatible bolts and a tube of anti seize, and lucked out that the stud I nailed with the cutting wheel earlier still worked with minimal persuasion.

Yanked battery negative, waited 5 minutes, drove perfect. No idle issues, no downshifting issues, acceleration I've never known it to be capable of - over and over again. Drove it for an hour beating the piss out of it around town and on the highway, occasionally turning it off and back on to make sure I wasn't going nuts. Seems good.

I'm still going to replace the cat and get a Denso sensor on the downstream.

What came off
Unknown age
Part #21109601
Internet reveals Denso o2 sensor for a 06-07 Passat.
Very little mention of this part # across the web, just like the MAF and fuel pump part numbers.

Jesus Christ! You have enough parts on your truck from other vehicle brands that you might not even qualify as being a genuine Toyota anymore...

Now you are getting somewhere! As long as it drives good and passes emissions I do not think you have to change out the cat. I wonder where he was getting all his parts from? Also was thinking it was an import model and not a US model

Hah! Happy that I've swapped it all to Denso OEM stuff with part numbers confirmed on here. I'll make a Toyota out of it come hell or high water

I also am baffled by this, why would you go through the expense of using Denso products but pick the wrong ones? I can't imagine these were OEM part numbers 17 years ago and then swapped out, you'd think there'd be some connection to be found googling, on message boards or wherever.

One of the most obvious changes I've noticed in my now two drives of the car since replacing last night - is the idle.

My idle per Torque app, warmed up, sitting in [D] at a stop light, was always fluctuating. 590, 620, 605, 595, etc. Every time the display refreshed on the torque app (I think I have it set for .1 seconds), it'd be a difference of up to 30 rpm.

I figured this was because of Torque just being sluggish in the values it pulled, or that to be normal fluctuation - because you couldn't really see the needle moving up and down on the cluster. Post-sensor replacement it fluctuates +- 3 rpm. Just THREE. Feels gooood. I didn't realize how much racket my engine was making for years until I hit the highway last night and heard how loud my duratracs have become

So to anyone who finds this thread wondering if their 3.4L Toyota is eff'd up:

1) Drive someone else's to have a comparison
2) Clean up rust and PB blast everything, just because some day it might pay off
3) Understand that a car can be more or less undrivable and not throw a CEL, somehow.

It sucks that I put so much time and money in to it trying to fix something simple - but I do have the peace of mind that comes along with having replaced a ton of stuff myself using top quality components. I don't want to jinx myself and get t-boned on the way home... but I'm suddenly extremely confident in this truck lasting me years and years, especially with the low mileage I put on it every year.

Break down of everything I've done to try and make it run top notch with no benefit - all correct part numbers used for my non-CA emissions '99

Under hood cable slack
NGK plugs
NGK blue ignition wires
PCV valve & grommet
Intake gaskets
OE radiator, OEM thermostat, red coolant
All soft lines under the hood replaced with silicone hose
Transmission drain and fill x 238942
MAF cleaning, MAF replacement
Throttle body cleaning
Fuel pump
Fuel filter x 3
Lung full of exhaust trying to see if I had a HG leak

Amazing. Good to hear that it is apparently fixed. Who would have thought...
Welcome to the wonderful world of PO's: It is useful to remember that there are, by definition, as many people with below average intelligence as there are with above average intelligence.

Man I wish I pressed you hard to take care of the bolt on the O2 sensor sooner. I really hope that putting the correct sensor for the vehicle in there solves it for good. It was fun to watch you go through the process of elimination. I have to do a lot of troubleshooting for my job. If it's a complex system the first thing I ask myself is "what is the simplest thing that I'm overlooking". Sometimes I find that first try and solve the problem in a short time. Sometimes I miss something and spend hours scratching my head. In the end it's always a great feeling to fix it.

Who could have known... wish I had thought to check it 3 years ago lol. Had it gone in the day I installed the MAF like I had planned, I wouldn't have these bruises and fond memories of dropping the tank Not all bad though since I cut my vent tube while in there and extended my range by 60+ miles.

Can't say the process of elimination was fun over here haha. Valuable experience though and it bought me weekend days to wrench in solitude.

Too true pluton - I bought a commuter car several years ago that I quickly discovered had a non functioning air conditioner. Relay was upside down in the fuse box, very intentionally done lol

Your long term short term fuel trims weren't off the walls?

Is there supposed to be an o2 sensor or a\f ratio sensor upstream of the cat?

I know the technician talked about that for a second when he had the diagnostic computer hooked up, but he didn't identify it as a problem - he was just explaining various readings

I had tried to log that in torque not knowing what I was looking at, with the plan of assessing on my computer... but the logging feature in torque is pretty awful

If your 1997 4runner is non-California emissions (which should be on a sticker under the hood), then you would have an o2 sensor

Probably why it didn't throw a code. usually if those numbers off you will get a code. based on my reading, it seems those two go hand in hand. but there are other reasons too.

My hood was replaced, so there is no sticker. I believe there is only one cat though.

'97 is all one-cat, even in Cali.

Good to know, I bought this in California, Cali website says it was smogged from 2001 to 2010. Still not sure where it was originally bought from.

@hour, I gotta hear this straight from you bro. You went through 100 hoops and the problem was a front 02 sensor that was a Denso meant for a VW?

This can't be real.


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