If you didn't reset your computer, reset it. That would be a good first step.
Disconnect negative cable from battery for 15 minutes. Reconnect, start, let idle for 10 minutes (all accesseries off), turn of, start, let idle for 10 minutes (all accesseries on). See how it runs then.
If you've already done this, let us know.
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351W 89 Mustang GT Convertible