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New issue: rough idle/misfire when cold. ???

March 01, 2016, 04:17:45 PM

So,
It turns out I don't have all the problems figured out after all.
 After replacing the head gaskets, I've tracked down and fixed all the vacuum leaks, I bought a code reader and found that the O2 sensors were bad, so I replaced them. Now, all the problems that I've bugging you guys with are fixed, except that now it developed a new one.
Now it runs rough, stumbles upon acceleration, and misfires, but only when the engine is cold. Once it warms up, everything is great. It drives like a new car. The code reader shows that everything is fine. I'm at a loss.
Any ideas?
Thank you

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New issue: rough idle/misfire when cold. ???

Reply #1 – March 02, 2016, 04:35:45 PM

Is it possible that the idle air control is bad and giving the computer a false reading? How about the coolant temp sensor? I'm just trying to get to the bottom of this.

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New issue: rough idle/misfire when cold. ???

Reply #2 – March 02, 2016, 05:20:28 PM

If temp sensor is off calibration so the PCM is getting info engine is say 80* when it's actually 40* it's going to be lean when cold...

It's easy to verify the TPS is in spec, at 50* resistance should read around 60K, 16K at 104*, approx 4K at 170*... If it has a ACT, it tests in same way...

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New issue: rough idle/misfire when cold. ???

Reply #3 – March 02, 2016, 08:20:44 PM

Ok, I have one last question: I've heard that having some slack in the timing chain can cause surging when driving with light throttle. Can it also cause a rough idle/misfire?

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New issue: rough idle/misfire when cold. ???

Reply #4 – March 02, 2016, 08:23:16 PM

This is an intermittent issue. It will idle for a while just fine, then I'll drive it a little bit and then it will cough and sputter when I let up off the gas. Sometimes it will do it after I've come to a stop. I honestly don't know what else to try.

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