Is your AC low on Freon?
The PCM maintains two idle trim settings. AC=on and AC=off. If the system is low on Freon (or the outside temperatures are very low), then the compressor will cycle on/off due to low suction pressure. The effect is the PCM can not re-learn a new AC=on idle trim value.
One possible solution is to temp jump the low pressure switch and allow the AC to run for a few minutes. The idle quality should improve once the new AC on values are re-learned.
2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.