2002 Wrangler, 4.0. It's been idling high at cold startup, about 2000 RPMs and then gradually drops down to normal idle speed as it warms up. We took it to our mechanic and he diagnosed as a faulty coolant sensor, which he replaced. It did not solve the problem and the jeep still idles high at startup.
Today the CEL came on, codes P0135 & P0155 (O2 Sensor Heater Circuit (Bank 1 Sensor 1) & O2 Sensor Heater Circuit (Bank 2 Sensor 1)). I'm sure the codes are related to the idle issue, but not sure how. Is there a bad O2 sensor, or something else? Any ideas welcome.