cel,p0301, some days light is on then off

What is your question?

we have done a tune up, new coil, new gas cap, new injector, it will run great, start fine for a few days and then acts like a misfire or rough idle on cold starts then after about one minute it behaves normal...been doing this for 4 months.Sometimes it will do it on every start and then it will be fine for several days...???? I notice that when I take my gas cap off there is no pressure release( my other car releases pressure when cap comes off???)