Need advice! 2004 3.4L A/T, P0031 code, now stuttering/hesitating on acceleration

I have a 2004 3.4L A/T Taco with 198,000 miles on it.

My wife drives this mostly around town, and it would have to catch fire for her to notice anything going on with it. So I don't know how long this has been going on or how it's progressed.

However...

This past week, it threw a CEL and the code was P0031 (bank 1, sensor 1 o2 sensor right?) I figured that was something I could replace, but the store didn't have it in stock. We're in the midst of a move, so I figured I'd just get to it after we were mostly moved in.

Well, the past 2 days when I've driven it to bring stuff back-and-forth, this condition is VERY noticeable. Here's how I can best describe what it's doing:

-It idles fine

-From a stop, unless you stomp on the gas, 60-70% of the time it will "hesitate" when giving it normal gas. Kinda like you're not giving it any gas at all. Then if you hold your foot on the pedal with the same pressure, it will eventually start to accelerate. But it's almost like I have to let off the gas, and then try again for it to "catch"

-Driving in slow traffic, just trying to keep the speed at around 35-40 with my foot not pressing the gas pedal down much, it goes in and out of maintaining speed. What I mean is that it does that same behavior as I described from a dead stop acceleration while holding light throttle in normal driving. When it does that, and I push the gas down a bit more, it will often just do nothing until I either (a) let off completely and then stomp on it or (b) kinda pump the gas a bit until it "catches".

I had to replace a headlight, so I'd unplugged the battery for a few minutes to do that. The CEL hasn't come back on since being reset by the unplugged battery, but the behavior has gotten worse.

Any guess as to what is actually happening? I'm assuming I still need to replace the pre-cat o2 sensor. But does it sound like something more serious? I'm just trying to gauge whether or not to take it to a mechanic and roll the dice with what he decides it needs or try something myself.

Thanks very much in advance!

 

Change the O2 sensor first and foremost and go from there....

It's easy to change. I made a write-up for a manaual tranny - not sure how this will relate to an Automatic.

http://www.lieblweb.com/o2replacement.html

The O2 sensor plays a very important part with emissions and sends data back to the computer. The computer will then adjust how your truck runs.

 

I had the same symptoms when my 02 sensors went out around 185K. After replacing both of them my issues were resolved. My truck is a manual but it was a very simple replacement so I'm sure you won't have any problems. I never got my codes cleared from a shop so from time to time my CEL will come back on and throw the same code for 02 sensor but i just ignore it.