Hey ya'll, long time lurker, first time poster, and love all the info you guys have! I have been a happy owner of 2000 Toyota 4runner limited, 4WD Auto, 3.4L 5VZ-FE V6 since I drove it off the lot for the last 120,000 miles. Have done regular oil change every 5-10k with mobil1, and new timing belt in '07. My cat converter went bad about 2-3 years ago, so I've had to reset ECU before inspection each time cuz its a dual cat system for Cali emissions, which is wayy overpriced imo. New 02 sensors did nothing, so that's why i left it unchanged. CEL has been on this whole time, but performance/mpg has been great, until now.

Recently, some new issues cropped up, and engine feels sluggish, almost restricted, at rpms over 3k, and acceleration is poor above 3k. When I reach about 50mph, the Overdrive gear kicks in i believe, but it feels pretty rough, and a lot of stuttering is felt. It's jolting, and you can feel the power loss. Also can hear it misfire when accelerating hard, and check engine light blinks alot. Once I get to around 55 the stutter goes away, unless i gas it hard again and more misfires happen.

I took it to my mechanic, and he got a bunch of error codes: p0171, p0300, p0301, p0302, p0420

He thinks the cat is breaking down and clogging the exhaust, causing engine to run lean, causing misfires, and poor performance. The stutter with the OD gear could be the trans or torque converter going bad. I'm now debating if i should dump alot of money to replace the cats, 02 sensors, plugs, coils, wires and all fuel injectors and hope the trans issue goes away. My mechanic thinks the trans could go bad soon and suggests selling the car while its still running.

Sorry this is so long. What do you gurus think? Could the trans issue go away? is it even a trans issue? Thanks for your input!

How long since you had a good old fashioned tune up? Plugs and wires?

p0171 - see the recent post on this code. Try cleaning your MAF

p0300,1,2 these are your misfire codes. 300 is random, 1 & 2 are specifically for cyl 1 & 2. This could be plugs, wires, coils/boots or injectors.

p0420 is normally associated with the rear O2 sensor I believe. You said you already replaced them (both?) right?

The stutter with your trans is most likely the misfires not a tranny prob.

The concept behind the flashing MIL light is that your misfire is severe, with the risk of unburned fuel causing damage to your cats. The good news is that fuel can screw up the new sensors, too. So maybe your cats survived and it is just your rear O₂ sensor. Or maybe both. Which code were you clearing every year? If it's the misfire, cats are probably dead.

Resolving your misfire is first priority, as you really can't evaluate the tranny (especially over the internet) with a motor that's having fits, nor can you deal with the P0420. Start with plugs and wires and clean MAF and throttle body. If that doesn't do it, I'm thinking injectors because 1 & 2 are not on the same coil pack. You need to do this anyway because it will be hard to sell in this condition.

I agree 100% with the other 2 guys, I think these spark plugs are supposed to changed at 60k and if you haven't done them yet you've been on barrowed time for a while. Have you had the timing belt done at all?

My mechanic said the plugs looked fine. The wires and coils are original I believe, unless they change them for standard maintenance (60 or 80k I think), but I'm not 100% sure. When my cat went bad 2-3 yrs ago, the shop changed the sensors and the CEL came back on after 2 days, so they took them back and the originals are still in. They didn't clarify if they changed both or just one. If I understand correctly, one is a air/fuel sensor in the front and 02 sensor in the back, right?

When I went for inspection, I would just disconnect and reconnect the neg battery wire, drive ~10 miles to populate the ready codes before the error codes came in.

If I wanted to use a federal cat, would I need to swap out the ECU as well? Would that be cheaper than dropping 1900 on the dual system here: 99-02 4Runner 3.4 V6 Catalytic Converters CA Emissions | eBay Can anyone recommended cheap cat that my ECU will not reject after a while, cuz I have read about some horror stories about that.

I'm so overwhelmed with how much this could cost to fix. I'm gonna try cleaning the MAF and getting new plugs and wires. I hear Denso is the way to go. May also get seafoam to clean injectors. If that doesn't take care of it then I guess I have no choice but to get new cat and sensors. Is that a good approach, or should i check other things? I don't have a garage or the tools to do this stuff, thankfully I have a great mechanic (through my gf hehe )

Also, will it be safe to drive as long as i stay under 3k rpm, or just don't drive at all? Any driving would be in the city. Thanks everyone!

Timing belt was changed in 2007

Yes, because the federals use an O₂ front sensor, that is very different from the Cali. type A/F sensor (which you would also have to change.) However 1), here in NJ, they run your VIN on a database--they will know it was a Cali. If the ECU reports Federal, the computer will flag you--and 2) it is against Federal law to alter the emissions characteristics of a vehicle from factory, regardless of the state in which it is located. You would have better luck with a Fed cat and a URD simulator to fool your Cali. ECU, also illegal, but cheaper and better chance of getting away with it.

I just about had fallen off my chair after I saw how much the 2 cats are to replace....So in Cali the only legal choice is paying $1,900 for replacements? I know the cats here need CARB #'s to be legal, but doesn't Magnaflow make one?

Well I'm in PA, so I've been able to get away with inspection by resetting my ECU, but idk how much longer I can keep that up, since i got alot of other problems now. Next inspection is due in july. I'm so pissed this stupid cat is so overpriced, and that i need two!!

Anyone near Philly interested in purchase? I hope to get $9k for it, the body and everything else is in really good shape, just put new brakes and Michelins in December, and I've been the single owner. Its such a shame, this engine still has lots of life left, but its going to become too much to maintain for me. It could be a simple fix I suppose, but I don't have the time nor tools to do it myself.

That is hard to deal with...Good luck with everything!!