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Hi thank you for your question hope this helps.
P0135 = O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
P1399 = Random cylinder misfire.
This code refers to the front oxygen sensor on Bank 1. The heated circuit in the oxygen sensor decreases time needed to enter closed loop. As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The ECM tracks how long it takes for the oxygen sensor to begin switching. It the ECM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135.
A code P0135 may mean that one or more of the following has happened:
This is caused by a clogged EGR valve ports.
Sorry you are right the CRV did not have an EGR system.
P1399 = Random cylinder misfire
P01399 is a misfire code, you have replaced all the parts that are related to the spark plugs so we know that is not the problem.
Have you had a compression test if the cylinder compression is to low do to wear.
Next i would check and adjust the valves CR-V intake valve is 0.003-0.005 in. (0.08-0.12mm). CR-V exhaust valve is 0.006-0.008 in