My van has been running just fine. Went to start it after not driving it for two days and it wouldn't start; it would just crank but wouldn't turn over. It sat for two days. I tried starting it each day but got the same results - crank but no turn over. Day 3 - tried starting it and it turned over just fine and seems to be running normally. I am a little hesitant to trust it - wondering if it is going to die on me somewhere. Thoughts on what the problem might be?