OK so i go to start my truck and it is idling horribly. i start checking spark plugs, injectors etc. replaced spark plugs and still wont help anything, the only cylinders firing are 1 and 4. 2 and 3 had oil on them when i pulled out the old plugs. then my check engine light came on around the time that i started it up and found the idling problem, i ran the code and it said bad o2 sensor, i figured no prob, replace it and everything will be fine. i replaced it but nothing changed, it still ran the same code and the idle is still sh**.


also a random thing happened as well, my speedo indicator is all the way on the right hand side and now will not show what my speed is. i need help!!!....... and this is my first post so hi guys!

any help at all would be greatly appreciated guys. im semi knowledgeable about my truck and motors in general but im stumped on this one.

What year truck?
What engine do you have?

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Hmm, too many unknowns.
Year, type, mileage, trans, DIST/less, COP,
The year is a biggie here.
Idling horribly out of the blue immediately at start up? Perfectly normal previous to this?