ORboater

First time poster many time user - removed and rebuilt starter contacts and replaced a cracked exhaust manifold thanks to the help of old posts and everyone out here. Cant speak enough for how great this site is.

I've Got a new problem that i could use some help with:

I have a 1999 Taco 4wd with 160k miles on it and she's hurtin a bit.
Engine light came on months ago and showed a bad O2 sensor (bank 1 sensor 2). I left it alone simply because it was downstream of the cat and didn't effect fuel efficiency much (maybe a mistake, but i'm a poor/cheap college student).

Its been idling extremely rough lately and on a trip to CO from OR the millage went from 19mpg to 15 and finally the CEL light came back on. Once read, it showed a faulty O2 sensor (this time bank 1 sensor 1) and PO302 - random misfiring of Cyl. 2.

So my questions:
Whats the chance that the faulty O2 sensor is causing the PO302 error?
Fuel filter, plugs (spaced correctly) and wires were replaced about 10,000 miles ago - could it be in the coil packs?

I did use Bosch plugs and after reading enough threads here i'm planning on swapping them out for Denso's

And finally - here's a picture of the O2 sensor and bolts (i couldn't figure out how to insert a picture so follow this link) - The truck was driven in NH for the first 120k miles so its seen its fair share of salt and the 12mm nuts are more or less non-existent. Anyone got any clever tips on how to pull these things off? cut? torch? hack? I'm trying not to kill the threads so that the installation the new O2 sensor is easier.

97ltd4x4

Sounds like multiple problems to me,you need to take care of your p0302 misfire first.Do you have a 4cylinder or v6?....Next would be get the bosch's out of there..You could have a bad coil pack,switch it with another one to see if the code moves to another cylinder..if it does you found it...if not,could be wires,injector,compression,ect..

Next the sub 1 O2 sensor,there was a thread not too long ago about getting the rusted nuts off.Use small ignition pliers and crush the nut/or carefully use a hammer and a chisel and chip the nut off..Then run a die over the threads to clean them,and do not forget to have new nuts on hand before you do any of this...

The sub2 code usually means cat is trashed,your misfire code could have caused this.But,you have a 50/50 shot at it not comming back once you get it running correctly.

kosmindtrip

i have the same problem...po302 ...i replaced plugs ngk plat...new wires...cleaned maf sensor...replaced o2 sensor with no affect....could it be the cat had heated up and fried the o2 sensor.?..kinda what im thinking but im no expert?????

ORboater

Its a 2.7L 4 banger. I'll get the plugs out and switch the coil packs around tomorrow morning and let you know how that goes.

TRT4Runner

On the corroded o2 nuts. I ran into the same problem. The nuts were pretty much nonexistant. I had a new A/F snesor and procrastinated on installing it because of their condition. I had sprayed the %&*$ out of them w/ PB Blaster for two days and had no room to get anything on them to get them off. I was planning on using a dremel and cutting the nuts off. I said screw it and took it down to Midas and for $30 and a 1/2 hr later they had them off and the new one on. Well worth it in the time and energy I didn't have to expend. I love working on my cars, but with a toddler at home, it isn't so much fun anymore when I don't have unlimited amounts of time to do things......

ORboater

Took the plugs out and to my surprise i had Denso plugs already in there (things you forget when you're a student), replaced them with new ones since i was already wrist deep in the process. Cleaned the MAF and the throttle body and reset the CEL. I've driven around 4 times today, up to 30 minutes and on both highway and stop-and-go without the light coming back on. Waiting to see what it says when it does then i'll switch out the coil packs if necessary. It's still idles rough though so i'm guessing that i havn't fixed anything and just need to wait for the CEL to light up again.

In regards to changing around the coil packs - can i just leave them mounted and just switch the wires (both the ones that go to the plugs as well as the one that goes into the coil)? or do i have to take them out, switch them around?