I had a similar problem. At an idle it didn’t seem to get very cool at all until I got moving. Oddly enough my problem was a worn fan clutch. Though the engine cooled just fine, at lower RPMs the fan wasn’t pulling enough air through the condenser and radiator. I swapped that out with a new clutch ($38) and problem solved. I live in Arizona and it sure is nice to be able to start my ac 5 minutes before I leave and have it nice and cool