Ok, I bought the 98 Acura TL 2.5 for my son in Sept and I have ended up doing more work on it than I anticipated, but it has been fun. I will post more info on my DIY water pump, timing belt, thermostat and accessory belt changes.

Tips for the O2 sensors
Check online prices! Don't just go down to Autozone or Advance Auto parts to buy the stuff! amazon.com seems to have the best prices for auto parts right now. Yes, amazon.com. If you have the Prime membership, the stuff usually gets to your house in 2 days with free shipping.

After using these parts the P0141 and P0130 error codes were taken care of. Oh yeah, disconnect the battery and take the spare radio fuse out momentarily to clear the ECM codes. Put the fuse back in.

Downstream O2 Sensor: Denso 234-4209 $28.50 Took about 1.5 hours. It is a 4 wire sensor. The connector is under the passenger seat. The cat heat shield bolts were rusted on so I pulled the thing off. I didn't need the O2 sensor tool for this one, just popeye arms and a wrench. The universal splice kit sucks compared to the Bosch one, I just reused the one that was already on the car from the previous owner's replacement.

Upstream O2 Sensor: Bosch 15730 $33.50
Took 1.5 hours to replace. Had to take out the battery, battery tray and use the smart connector to splice in the new sensor. Found out that whomever replaced the sensor before, did a hack job of spicing the connector and reversed the positive and negative wires. It is a 4 wire sensor. . I had to use the O2 sensor socket as the exhaust heat shield wouldn't allow a wrench access to the nut surfaces. Got it off amazon.com, works perfectly!

O2 Sensor tool: amazon.com again. TEKTON 4929 3/8-Inch Drive by 7/8-Inch Oxygen Sensor Socket. Works perfectly!

 

I just did mine last week except I used RockAuto.com for my parts (AWPI I think). They were a little more expensive, but I didn't have to splice/solder anything and it took a little over an hour to do both. I had done the research with the shop manual beforehand, so I knew the procedures. I only got the one downstream code (after a Seafoam a few months back), but I went ahead with 2 new ones since to replace the factory originals.

 

i also ordered mine from amazon.com... i initially went with oxygensensors.com but they d!cked me around for weeks without updates... amazon got it to me at prime speed...

 

I purchased twice from oxygensensors.com.
I did not have any problem, but little pricey.

Amazon with super saver is lightening fast, no doubt.