Chugging when idling

My 2009 Focus with 270,000 km on it is chugging a lot while idling, especially on hot days. It sounds like it might stall at traffic lights. My friend cleaned the spark plugs yesterday, but it’s still doing the same thing today. Any ideas on what might be causing this?

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don’t think it would hurt to replace all 4 ignition coils…they’re cheap and easy to replace.
I’m surprised you’re not getting any check engine codes.

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Free advice cleaning the spark plugs won’t help much. When he took them out, was there a lot of oil on them? If so, you might have a bigger issue. Otherwise, follow the other suggestion and get some new spark plugs (about 40-50 bucks atleast) and replace them.

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Yes they had a little bit oil on them

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We resealed the gasket a few years ago

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Given the high mileage, it could be a fuel system issue/dirty air filter. Be sure to inspect the fuel filter and air filter

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Checking for the idle air control valve or throttle body. Heat might be the problem