car won't always start right away on 2001 Kia Rio

the car will backfire and whine when trying to start it. then the engine light will come on. it was towed to a shop and they put it on their machine and no codes are coming up. they are able to start it all the time.

The check engine light could come on when the engine stalls and not set a code, but if the light is on while it's running, then there should be a code. I would go down to the shop and start the vehicle a few times with the mechanic who looked at it. Try to get it to happen and see if the light is on when it is running.
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check misfiring. i mean the order of firing in the 4 cylinders.. but sure the spark plugs are in good conditions and in the right place of order.