Isuzu 91 headache

Ok needing some help out there........i have a 1991 isuzu rodeo 3.1 litre thats been giving me grief lately.......basically idles fine but does not want to pick up speed when you give it gas....in the last week
ive changed the o2 sensor and the temperature control sensor and the ECM still reads o2 sensor circuit. When the codes were first read it was a code 44 which is lean....changed o2 sensor then temp sensor and now it reads a code 13........no clue where to go from here.......anyone out there have any suggestions ???
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You may have up to 3 O2 sensors, one on each exhaust manifold and one after the catalytic converter. Because a '91 is pre-ODB-II I can't look those codes up for you. Do you know what code 13 indicates? Also, I've hears of new O2 sensors not functioning correctly, but that seems like a long shot to me.

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2 other possible areas. 1) The fuel filter. 2) The ignition coil. To check it, first locate it in the light, then when it gets dark, start the engine and look for any sparks or arcing from the coil. You may have to rev the engine a little to get it to "leak."
Ya the code 13 is the o2 sensor circuit,that is not the same as the lean code.I have now changed my plugs and wire cap and rotor as well,and sill no change.I did find that the o2 plug had come un pluged,but all that did is stop the codes.Still does not run right,any more ideas?????????

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