97 4.2L Having cold start troubles

My 97 F-150 with the 4.2L V6 is having troubles with starting when it's cold. Last weekend I drove it all day Sunday with no problems. Monday it sat idle and when I went to start it Tuesday afternoon, it could crank but would not fire. It seemed like it was loading up so I held the accelerator to the floor to clear it out. It started to pop like it was backfiring so I let it sit for about 20 minutes. Tried to start it again, same thing. Let it sit 20 minutes, same thing. It kept getting closer to starting and finally on the 4th or 5th try of that, it finally fired and ran rough for about 30 seconds and then idled fine. I let it warm up and it drove perfect. After about 5 minutes of driving though it did through a check engine code. I work in an accessory shop and recently put on an air intake and throttle body spacer. We have never had trouble with starting however on the vehcles we have done. The truck has had the air intake system for at least 2 weeks without problem. The truck now has started to act like it's not going to start in the mornings now and not sure if it sits for more than a day if it will act up again. The temperature around here is now below 25 degrees every day. Anybody have any ideas where to start? The truck has 81,000 miles on it and I love it but need to get it more reliable.