94 Explorer not starting consistently

94 Explorer is not starting all the time. Most of the time when I hit the switch it starts right up without any hesitation and runs smooth once started. Lately, it may or may not start. The motor turns over but sounds kinda like the old cars when they were out of timig a little. It may not start for 4 or 5 tries....then it will start. Again, it runs very smooth. Sometimes I've let it sit overnight before it would start again. Ive read some of the previous post and not sure if my problem is the same as some of the others. We've had it in 2 shops and they tell us they cannot diagnose the problem if it starts. Unfornuatley each time its been at the shop, it starts. Any ideas? Thanks