Long crank/Intermittent starting issues?

BWRIGHT26

MEMBER
2013 HYUNDAI SONATA
260,000 MILES

Long story short I used some Lucas stop oil leak in my car and afterwards developed a long crank start. Sometimes it starts right up. Other times it takes awhile. I am also having low gas mileage. After car starts it runs perfectly fine. Has thrown no CEL either. First thought was HPFP but that was replaced and didn't fix the issue. Thoughts?

Thursday, February 26th, 2026 AT 8:58 AM

1 Reply

AL514

MECHANIC
5,556 POSTS

Hello, this being a GDI engine and the high mileage you have, I would say the intake valves are probably very gummed up with carbon if they have never been cleaned. Its pretty easy on the 4 cylinder engines, but Hyundai's seem to be one of the worst when it comes to carbon build up on the valves. To check them I pull the spark plugs and put a bore scope down into the cylinder and look at the valves while they are open, you can see carbon build up on the valve stems. Its a regular service now to have them cleaned with either walnut blasting or some other chemical means. I would check the oil too for gasoline.

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Thursday, February 26th, 2026 AT 2:10 PM