Flat spots/Engine hesitation after O2 sensor change

03' 3.4L V6 5 speed, 130k miles

Hey y'all.

First post - tried to search but couldn't find anything very specific to this. Bought the truck about a month ago from a local guy. Check engine light was on for upstream O2 sensor which he agreed to buy and send me. Truck ran well until this past weekend when I changed the upstream sensor. CEL is off now and I took it for a spin. Once i was out of my driveway the engine seemed to hesitate in the mid range RPM's and lurch like the power train was struggling in all gears. No lights yet. My initial thoughts was spark plugs/wires but this seems very coincidental to notice after changing the sensor. Any ideas

Thanks
Jake

 

Swap back old sensor . See if it goes away .Could be coincidental. Went through a few episodes like that . Also check for pending codes .

 

You may have inadvertantly replaced the A/F sensor with an o2 sensor. How did the replacement part compare to the one you took off? A/F sensor is always up stream, has fewer holes and costs 4 times what an o2 sensor does.

 

Welcome to YodaWorld

 

OEM Toyota sensors are DENSO. Lots of cheaper aftermarket knock offs which are a waste of time and money, Do you think the seller would pay $249 at the Toyota dealer or $49 elsewhere?

 

The exact same thing happened to me when I changed out my upstream O2 sensor. What I did was slowly drive it to the interstate. Once I got on the highway and floored it the truck seemed to clear itself and run fine thereafter.

 

Gave driving on the highway a shot. Didn’t make a difference. Changed back to the old o2 sensor and the CEL came back on but the truck ran like it used to. Here’s a pic comparing old to new. Assuming they sent me the wrong one. New on the left.

 

I would assume the same thing.

 

I believe the upstream is a air fuel sensor, the downstream is the o2 sensor. You may want to compare on Denso website. Also, I would replace both.

 

I bought a set of Denso's from RockAuto.com last summer for my 99 PreRunner that work very well. The part numbers below are for an automatic PreRunner. You may have different part numbers.

IIRC, I had to lengthen the cable for the downstream sensor. I think automatic PreRunners use an extra long cable. Though, it worked without issue.

Over the years, I've purchased at least a dozen Denso or NTK sensors from Rock. No issues.



RockAuto discount code link.

https://www.tacomaworld.com/threads/rockauto-discount-code-introduction.86042/

 

If a catalytic converter is partially plugged it will cause close to the same symptoms

 

Resurrecting this thread, because I had the same issue after installing an aftermarket upstream o2 sensor. Initially it ran good, but now I'm getting that hesitation and lurching. Its super weird too, because it doesn't seem to affect the rpms, it only feels like its struggling. Going to go with oem o2's like I should've, swap out both at the same time, and update on if it fixes the issue. If worse comes to worse, might need a new cat, but it only started after the o2 sensor.