My check engine light was intermitant during the summer so I ignored it till it came on and remained on. Numerous codes. Changed MAF and plugs ($650) New code P1135. (Bank 1 sensor 1) Replaced that at dealer ($475. can). New code P1135 (bank 2 sensor 2) Replaced that myself (oe denso part $140.) Noticed that both the A/F sensors were coked up.
New code P0136 (bank 1 sensor 2) All these within a couple of weeks.
Plan to replace Oxygen sensor myself and see what happens.
Any comments/suggestions?

 

Welcome to the Club.

The sensors can get coked up and old. I mentioned a few posts back about my getting a P1135 and using something called PowerBoost, a cleaner by a company called Nology (famous more for their spark plug wires), but I have also used something called Gas Extreme, (both go in the gasoline) and they are pretty potent if used on a half or 1/4 tank and can blast a lot of that crud off the sensors, cat and pre-cat, improving mileage. Something else I use, though not quite as potent (nor as expensive or difficult to get) is a full bottle of Techron with a full bottle of Restore fuel injection cleaner on a half tank.

However, when the vehicle is older the sensors are of course older and they can get dirty and die, and sometimes no amount of cleaning will keep them from going off the fritz. So replacing them was the right thing to do there after you verified they were truly dead.

Well that P0136 is a different type of sensor that is located after the catalytic converter underneath your RX. It usually has a longer life than the two A/F sensors. If you have continued to try to reset the CEL and it still prevails then change it out.