silvertaco4X4

Hello all.

Truck threw a P0420 code on Wednesday night. Catalyst Efficiency Below Threshold (Bank 1). Had the code cleared and it hasn't come back on since. Driving the truck today, about a mile from my driveway, RPMs go up and stay at ~2000 at a light and I'm thinking "great, what now". At the next light they start going up and down repeatedly between 1500-2000. Pulled into a parking lot and shut the truck off, and then when I started back up and everything was normal again. Ten minutes later it's doing it again at another light. Shut the truck off and all is well until I get home from my short trip.

Drove it real quick again tonight and got the high RPMs again for a short time, then everything was okay after that and I haven't driven it since. I know the P0420 code is probably the cat or an 02 sensor, I'm just wondering if this other loping symptom could somehow be related. I've had an idle for a long time with this truck that I'm not happy with, but after trips to two different dealers they say it's fine. Seems to generally run crappier in the winter so I'm not looking forward to the cold.

Any ideas? I've read some cases online where 02 sensors caused some weird stuff like this with idle, so I'm guessing it wouldn't be impossible.

Thanks.

BATF

Your downstream o2 could be dead or on it's way out. It's there to make sure the cat is working since it's OBDII. How many miles you have on the truck and are you still running the orginal sensor?

jimbo74

before you replace the sensor, take a look at its wiring and make sure its connector is plugged in... since that sensor is run pretty much down the firewall along the frame to the exhuast, its possible it has heat damage or a short or worked itself unplugged....

TRDOLMAN

On the newer trucks the second O2 sensor wiring comes through the floorboard under the passenger seat. At least mine does.
The 2nd O2 sensor should not effect the actual running of the engine. The first sensor is another story. I would check that sensor. While your at it, just for kicks and giggles, clean your MAF sensor. The p0420 just gives you an area to start looking. It could be the O2 sensor or an actual cat problem.

silvertaco4X4

This truck is CA emissions, so I'm still trying to figure things out myself. From what I've read online (and looked at under the truck) I guess it actually has two cats and two sensors. I banged on the cat closest to the muffler and I do hear something moving inside.. but very small, sounds like a pebble inside. So maybe the second cat is gone. I called a place yesterday to find out how they test them and the guy told me they either drill two holes in the exhaust - one above and one below - and measure the gases coming from the cat, or they do the same thing I did - bang on it and listen.

I haven't done more than that yet because it's been raining so much here, I'm gonna go look at things a little more in depth this morning. The sensors could very well be original.. the truck has about 113k and I bought it with 75k. I haven't changed them, and I actually really want to now that this has all started happening. Is the first sensor an A/F sensor or really another o2 sensor? I wish my truck was Fed emissions, things seem so much simpler. It did pass emissions with flying colors in May though.

Thanks for the input. I'll post if I find out anything more.

BATF

I doubt his would be unplugged. Since if it's unplugged it would throw another code beside P0420.

MTL_4runner

Cats are tested for both blockage (ie by drilling the holes and measuring back pressure) and for efficiency (via gas analyzer).

Yes, your front sensor is an A/F sensor.

silvertaco4X4

thanks.

i crawled under the truck again today. no exhaust leaks that i can find and nothing seems out of the ordinary with the sensors or wires or anything else i can see. good amount of rust at all of the flanged connections on the exhaust though. the truck idled at about 2000 for a while when i started it up this morning (no signs of coming back down) so i turned it off and then back on and it was fine for the rest of the day. no more acting up and no more CEL so far. i suppose i might just take it in somewhere this week and have everything checked out. should the sensors be replaced at a certain mileage as a maintenance thing, or should i find for sure if they aren't working properly before replacement? i know they are a little pricey.

silvertaco4X4

oh and also, i did clean my maf sensor just a few months ago, along with the throttle body. i might have a go at the maf again after work tomorrow.