O2 sensor issues

[VREN]

Hi, I bought a 1991 ls400 with 150,000 miles and recently got myself a check engine light. Code 25 and 26. The car would shake on idle as well. I went through forums and decided to replace spark plugs and wires. That didn't help so the next step was O2 sensors. Replaced both upstream sensors with Denso branded ones. The car ran perfect after that for about 2-3 days and then the problem came back. It wasn't shaking as bad at first but now we are right back where we started. I know coolant leaking in the exhaust can cause O2 sensors to die and I did have to add some coolant a few weeks ago when my light came on. (the shaking problem was already present at the time). Thanks in advance!

[paulo57509]

With OBDI, the trouble codes that are set don't necessarily point directly to the problem.

You have two codes that indicate both a rich and lean condition, meaning the O2 sensors are reporting rich/lean mixtures that the ECU cannot re-adjust back within range.

I would start looking at a physical fuel problem.

[dcfish]

Maybe your catalytic converter is getting clogged or deteriorating ???