1999 Jimmy P0300 + P0147

Hi I`ve got what is seeming like a classic Jimmy 4.3 problem. Hard starting, rough idle and poor mileage. I initially had the P0300 codeand, as I needed
new wires, replaced them. Th e plugs were new last year with about 15000 Kms so I havent looked there yet( A job for this weekend). Idle/ acceleration is better but problem seems intermittent at times. A second read is now showing P0147(O2 Heater Bank 1 Sensor 3) Could the miss have caused my O2 sensor to go "bad" or could this code be a result of the miss and my O2 is reading the rich condition? I dont want to chase the problem with parts and certainly dont want to change out the O2 and "blow" the new one. Thanks for the input Jeff 1999 Jimmy 4.3 SLS 4x4 194,000 Km
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What rich condition? Neither the P0300 or the P0147 in any way relate to or indicate a rich condition.

Miss fires do not cause O2 sensor heater failures.

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Ok So I have codes P0300 and a recent addition of P0147. Service eng light was on before my wire change but reset after the change and my drive to work. . I believe my EGR isnt plugged as I can the scan tool to actuate it. From what I`ve read the rough idle can be caused be plugs, wires, coil pack, O2, EGR and Cat Convertor. It could also be a bad cylinder but before I get into eng rebuild, I`m just looking for any advise on which direction to head first. Should I be looking to replacing the O2 due to the P0147 for the continuing rough idle or be looking elsewhere? Either way I`ll be checking my plugs in the morning first. http://www.obd-codes.com/trouble_codes/generic/p0300-random-multiple-cylinder-misfire-detected.php
wrote:

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The P0147 is nothing more than an inoperative heater in the post cat oxygen sensor. It will not cause a missfire. Verify that there is proper voltage being supplied to the O2 heater circuit, if there is, replace the sensor, if there isn't, correct the open supply circuit.
The P0300 is a less than specific indication that one or more cylinders are miss firing. Could be spark, compression, or fuel related. A good scan tool will be able to show individual cylinder miss fire counts which would pin point the exact cylinder. Given their history, I'd be inclined to suspect the fuel injectors before anything else.
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