Okay, it could be a few things. The fact that it eventually starts leads me to believe there is an ignition problem or a weak fuel pump. What you need to do is check for spark and fuel when the engine doesn't start. Directions and a video is available on our homepage under the DIY section.
You will need a fuel pressure gauge to check the pump. Most parts stores will lend one to you. When the vehicle doesn't start, you need to see which is missing to help identify which system the problem is coming from. If the check engine light is on (I assume it isn't or a shop would have already found the problem) it would direct the mechanic to the problem. However, without the light, it becomes a guessing game. If you find that the spark to the plugs is missing, my first guess is a crank sensor. Or, you may find the fuel pressure is weak. The injectors require a certain amount of pressure to allow fuel to the engine. If it is just weak enough, the injectors won't allow fuel to enter. I have seen cars that will only start with starting fluid but then run fine until they shut it off again. A weak pump was causing the problem.
Now that I mention it, when it refuses to start, see if it starts with starting fluid. That way you don't need to carry around a fuel pressure gauge. If it starts, it is fuel related. If it still doesn't start, it is ignition related.
Let me know what you find or if you have other questions.
Joe
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Wednesday, May 3rd, 2017 AT 11:44 AM