Sometimes it starts sometimes it dosen't

I have a 95 Ranger, 150,000 mi, 6 cyl, stick shift.
I have had this problem for a few months, when I turn the key to the on pos. All the insturment lights come on, seltbelt check gage break check eng ect, if they all come on it will start and run perfectly, if all BUT the check eng lite comes on it wont start. If I let it sit all nite the next morn all the lites come on and it starts and runs fine, I have had a new fuel pump and filter put in, the key feels a little sloppy when I put it in but it acts normal, in the wont start mode the starter turns the motor over fine it just wont fire. It does this about every other week, wont start, its been a good truck but this is just wierd, computer scan shows only a egr valve problem and I put a new on on, still have the same problem. Help