Hello All:

Long time reader, first time caller...

Have a 1999 4-Runner with 140k on the clock. I average 18.124563625 miles per gallon every tank and it doesn't seem to change based on highway vs. city driving.

The O2 sensor(s) have never been changed. Do you guys think it would be worth it to go ahead and replace if my mileage is where it's at...

Oh yeah and it's a V-6, 4x4, Limited...

Thanks for the input.

 

I don't have a response to your question but I have a 98 with 140K too and I'm wondering the same thing now

 

I just changed mine at 200k when the Check Engine Light came on all the time with a code for the O2 sensor. Here is what I noticed after replacing:

1. Increased engine response when lightly pressing on the gas pedal.
2. Change in loads on the engine did not make RPMs fluctuate as wildly.
3. Upon starting, the RPMs settled much faster and starting was smoother.
4. Engine is smoother overall

So if you feel like your motor is sluggish and does not rev as smooth as it used to then I say go for it. If you feel like your motor runs like it always has and the CEL is not coming on for the sensor then I say wait. Hope that helps and I also hope someone who knows a little bit more about this stuff chimes in because I am just telling you what I experienced after getting a pre-cat O2 sensor check engine light and changing the sensor.

 

you need to read the data from each sensor to see how lazy it is, and then make ur decision. so you are going to need a DATA reader (not a code reader) to read the data and then you will need someone to tell you what the data means. just replacing sensors because it is time could be a waste of money if they are operating correctly! mike

 

looking for help before I go to a mechanic and start that process...98 4runner approx 170K miles...was running fine, literally all of a sudden at a red light the engine started running rough as if it was going to stall...it starts fine every time, mildly rough during idle in park but stutters when you give it gas until the RPMs come up...if you put it in gear it really gets rough and seems to be struggling but will drive and not stall...no warning lights until today the check engine came on...any suggestions or similar experiences...I want to resolve on my own if I can to reduce the cost...sorry for long thread and for any/all help

 

Let's not let dakodah's post above change the direction of this post as he/she wisely started a new thread...

 

My CEL has been on for about 20K miles...doesn't have the umf it use to have...very sluggish on WOT. I guess its about time I see whats up. I am in a 99 4Runner with approx. 75K miles.

 

Guys, these engines are extremely dependant on their sensors. If your Check Engine Light is on, don't drive too many miles before getting it checked out. A bad O2 sensor or bad MAF will throw off the fuel/air ratio and can easily destroy the catalytic converter.

Do not defer maintenance! It will cost you dearly in the long run.

 

That's why I got over 200,000 mi on my Taco. Take care of it and it will want to play when you do. I guess you are no where near La. I could hook you up to my computer and see whats going on.

 

just so you know, a downstream after cat O2 sensor is about $95 and the one before the cat is $170ish so if you don't need to replace them, thats a lot of money. I have 161000 miles on my pickup and my CEL went on and I got a code for an O2 sensor. I started with just replacing the after cat one and the light has not come on since.

 

That's interesting. I was told that the pre-cat sensor would go out more often because the cat converter would clean up a lot of the emissions before it got to the second O2 sensor. Also, I got a Bosch OEM style sensor (1st sensor) for $119 at Autozone. This is on a 3.4L mind you. I do agree that if you are getting a CEL then you should definitely get it checked out as soon as possible but it is not going to be catastrophic if you don't in my opinion. I was merely trying to say that if you don't have a CEL then you probably don't need to throw your money on a new sensor just yet. I was getting the light intermittently for almost a year and didn't change the sensor until it came on and stayed on all the time. The truck runs great now.
P.S. Potomacduck, I do believe what you say though, I am sure you have a whole heck of a lot more experience with motors based on your other posts that I have read.

 

If you are getting a very steady 18mpg then you're probably fine since it's consistent and pretty much average for a 4Runner that sees a mix of city and highway.
I get a steady 17 with a bit of a leadfoot.

 

interesting. the CEL has been on in my 97 SR5 4x4 for some time, according to previous owner. he had it checked out and sure enough it was one of the O2 sensors. so, i just reset it and have been driving it ever since. it came on once, but i just reset it again. i guess i should replace it soonish.

 

If its not broke, don't fix it!! Why spent hundreds of dollars when you have no CEL?

 

i have to concur... thats about what i get on a factory tacoma v6 4x4 and i drive 75% highway.. on long trips i can get up to 21 mpg on a good day.. i have 96k miles on mine.. for some reason in the spring i was getting a steady 20mpg and now its down to 18mpg.. i think it might have to do with the 100 degree days and lots of AC running full blast

 

Thanks! That's why I asked. I know the old "don't fix it if it ain't broke", but at the same time if I could pick up a few MPG by freshening up the O2 sensor, then it would justify over time. Not all replaceable parts could have as significant a payback as those directly correlated to my 50 bucks per week fuel habit.

Think about it...2 MPG x 15 gallons = 30 miles per week. At 3 bucks a gallon that's 4.50 per week. That's a 6 month payback on the precat 02 for 120 bucks!!!

Now, if I spend the money and get .000001 more MPG, then that = dumba$$.

 

I'm not trying to tell you what to do......but.......resetting the CEL will keep it from coming back on for a while, sometimes for months. This is a bad choice.

You maybe be saving 175 bucks by deferring maintenance, but you are rolling the dice with your catlytic converter. The dealership price is between $800 and $1,000 for a new converter, some 4Runners have two of them. Say hello to Mr. Big Bill.

 

I agree with the philosophy "if it's not broke don't fix it" but I will say that at 150,000 miles, I pulled my o2 before the cat and you wouldn't believe the crud in that thing. It turns out the MAF sensor was the cause of the cel but I feel better knowing the o2 sensor is new and clean.

 

i wouldnt spend the $$$ if i wouldnt have to.

 

double post, see below...