1133 monitors the front O2 sensor for 100 seconds and counts the number of times it crosses the rich to lean and lean to rich thresholds. If it does not switch enough times, 1133 is set. lean is less than 300 mv and rich is greater than 600 mv. Sounds like you have a bad connection or a bad sensor.
The most common cause of this code is when the sensor actually gets 'lazy' - usually from running leaded fuel or spilling engine coolant in the exhaust pipe. It can also show up if you lay your oxygen sensor wire on your header and it burns through.
The solution is a new oxygen sensor, then clear the DTC.
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