The AFR is controlled by several sensor. First, the air intake temp, then the MAF, and finally the O2 sensor. But also the engine coolant temp and the MAP. If the engine is going rich after up to heat I would think the ECT sensor may be bad. A test you can try is when it'* running bad, unplug the MAF, the engine will stumble as it switches from live data to internal tables. If the problem goes away, the MAF is the problem. Another thing I would suspect is the O2 sensor. With you having past problems causing it to run rich, this can over whelm the O2 sensor and wear it out.
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