Takes two to start

I purchaesd a 1999 XJ 4.0 that had been sitting for a few years. I repleced the fuel pump when I drain the old gas. I replaced distributor cap, rotor, plugs and coil. I have not had any problems starting the XJ until recently. It seem like the colder it is outside the harder it is to start. I've search the web but I have not found any good solutions to the problem. Can you help?

Your not maintaining fuel rail pressure - bad fuel pump and/or regulator.
Forgot to add leaking fuel injectors!

IAC,....Intake Air Controller. It could be sticking or bad. First remove clean then re-install. Also, clean inside the throttle body and the cavity where the IAC pintle valve sit.

try putting the key in the on position for a few seconds before you start the Jeep, if it starts right up then its the fuel check valve. Its a common issue