My wife has a 99 4 runner with 93k miles on it. In the past couple months it has been running really rough with the idle fluctuating upon startup and seems like it has no power for the first couple miles. About 2 weeks ago the check engine light came on and I ran it by Autozone to have them scan it and they told me it was a lean left bank something......and I needed a new o2 sensor. The next day I dropped it off at a friends of mine shop and since the dealer didn't have the sensor he just cleaned the old one and cleared the code. Well the check engine light hasn't came back on, but it doesn't seem to be running any better. Could an o2 sensor cause the issues I am describing?

BTW the waterpump went out about 1500 miles ago and at that time I had the timingbelt, all belts and hoses, and fuel filter replaced. The only thing I didn't replace were the plugs and wires.

 

My girlfreinds 99 just had a similar problem. It was throwing a code saying bank 1 too lean and throttle position sensor. It was the 02 sensors and MAF sensor. Do a search on here to find out exactly how to test the sensors with a multi-meter and that should tell you what sensor(s) are bad. It probably is one of the sensors

 

clean the maf and change the o2 sensor. at that mileage it was going to happen sooner or later so buck up and buy the stuff and get it over with..

 

I would have helped to know what the actual ODB code was but cleaning the O2 sensor won't help.
You should replace the O2 sensor and clean the MAF with brake cleaner.

 

"the dealer didn't have sensor in stock" that day or I would have "bucked up and bought the sensor." Would a o2 sensor cause these problems? Is the dealer the only place to purchase a sensor or is there a good aftermarket replacement?

 

Could it be the plugs and wires? how long have they been in? I have read some posts saying there was a world of difference when they changed the plugs

 

yeah i would do the whole kitten kaboodle.. new plugs, O2 sensor, seafoam and or techtron, and clean the MAF

 

no after market, make sure its DENSO or NGK or you will be sorry.. and yes its possible but guess what?? at that mileage its smart to go ahead and replace it

 

You don't necessarily have to go to the dealer to get the 02 sensor though. URD has them; that is where I picked up my replacement.

http://www.urdusa.com/product_info.p...s_id=430006000

 

Hey guys--just found this board! Im getting ready to replace my O2 sensor as well because of Sucky mileage and the fact it has 92K on it. I have no Engine light though but here I should change it out because of the sudden fuel drop.

My dealer wants $240 for the 02 sensor(Cali model) and looking at the URD website I can get it for 92 bucks--is that for real? Wow that is a huge differnace. Is that OEM that toyota uses the Denso ones?

 

Well after replacing the O2 sensor and cleaning the MAF her check engine light came back on today again. Does the MAF need to be replaced? I am about to run it by my mechanic and have him scan it and tell me the code I'll post it back on here this evening.

 

I had a similar problem. I had a check engine light and rough idle. Idle was also too low, and sometimes the engine would quite. I went to autozone, and I think the code for the engine light was p0171 / lean bank. I cleaned the maf, but this did not help. So, I took a chance and ordered a new maf. The sensor was just over $100. Fortunately, this completely fixed the problem. Sometimes, the maf just goes bad and can't be cleaned. In my case, I was using a TRD airfilter. The oil off the filter slowly contaminated the MAF.

 

I think the MAF part number is 22204-07010. Check Conicelli toyota at partznet.com . They usually have good prices there.

 

Could a loose crankshaft pulley bolt cause any of these problems?

 

Thanks alot for the information I guess I'll go ahead and order a new one. Hopefully it'll fix it.

 

Would yours run good when it was warmed up? She said she is only having problems in the morning and when it sits at work. Is the MAF the only other thing it could be?

 

It really didn't matter if my 4runner was warmed up or not. The idle was too low, and sometimes the engine would quit at a stop light. I reset the ecu, and the check engine light would stay off until I accelerated moderately. Then it would illuminate again.

 

check out this thread:
https://www.yotatech.com/forums/f2/p0171-again-100966/

In the end, this member went to the dealership to diagnose his engine problem. They charged him $400 to replace the maf.

 

Well after searching around last night I read the proper way to clean the MAF.......all is well now and running like new. Thanks for the help.

Justin