computer.. i can assume it's a 2.4L? The engine would be useful because a 2.0L is carb'd and a 2.4L is fuel injected and both have different reasons for running super rich. If it's fuel injected I'd look into a leaking fuel injector or maybe a bad ignition system like worn wires/plugs/distributor. Odds are low it's mechanical since it's got a new head. That eliminates valve issues.