2001 Hyundai Sonata--Rough Idle--White spark plugs?

doyou

New Member
Short and to the point:

This is on my friends car. It was idling rough. He changed the spark plugs. Old ones were white (read: lean fuel mixture.) CEL P0303 "cyllender 3 misfire" I measured the resistance of the spark plug wires. around 1700 ohms for the long ones and 700 for the short ones. I think that is within specifications.

Since the two coils are identical, I swapped them. the idea is, if the one running cyllinder #3 is bad, then by swapping them #1 should set off a CEL. (testing to see if I have a bad coil)

I reset the CEL and test drove it. 45 minunts later, I get a P0171 "lean fuel mixture" Sounds like a fuel problem... I doubt the fuel filter, or pump. Possibly clogged fuel injectors? Please let me know what this problem may be, thanks.
 
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