Hard cold starting, rough idle

I own a 92 Daytona 2.5L TBI with 282K miles. It’s been kept in great shape since I bought it new, by me. Last summer I replaced a leaky gas tank, with new fuel pump, sending unit, rollover valve and rubber lines. Unfortunately, I initially hooked up the fuel pump return line to the rollover valve and vice versa, as they’re the same diameter. I ran it for 1/2 hour at idle and corrected the mistake. Since that first cold start with the new tank, it idles at 1000 RPM on cold starts, never going high initially as it always has. As it gets progressively colder outside, the problem is worse, to the point that below 35F or so, I have to open the throttle to start it, and keep my foot on the gas for 30 seconds to prevent stalling. Then it’s fine, and runs like brand new when warm. Gas mileage is down from 34 mpg to about 29, and emissions failed by 20% over the HC limit. No fuel leaks. Coolant temp sensor reads proper resistance values. All other sensors seem fine, as do hoses and wires. Is it possible I damaged the fuel pressure regulator with the reversed hookup, so that the pressure is too high and it’s flooding on cold start?