My engine cranks but doesn't start sometimes. Once the engine is running the car runs fine with no problems. About 1 out of 10 times the car doesn't start while most of the time it starts just fine. The starter sounds like it's cranking the engine at the speed it should. Sometimes when the car doesn't start I'll just try again like 20 seconds later and then it will start. Recently though no matter how many times I tried it just kept turning over and not starting, but then jump starting it worked. It runs just fine once its working. Any help would be appreciated.