These may give you some other ideas of what to check. The link about the TechStream software showing the voltage values should give you something to check and may be why you are now getting the P0136 code after your extender was added. After looking through the above links the problem could be something on the intake side that could effect the exhaust. Any air leaks in the exhaust or intake, the MAF sensor, the idle speed controller, the flex gasket, non-OEM oxygen sensors, and non-OEM convertor can all cause the code. Things that stand out are the oxygen sensor voltage changes and the fuel trim readings. If you do not have the proper tools to check these things then all you can do is guess and that can get expensive. Toyota does this code different then other manufactures so watch what information you read as other manufactures will not deal with this code the same as Toyota. TechStream is Toyota factory software developed by Denso for diagnosing the on-board computers through the OBII port.
Thanks! I haven't had a chance to dig through those links yet but thanks for sharing em! I'm also getting a P0125 code as well now so I'm pretty sure the defouler messed something up. need to lift it up and check the wires for breaks first though...