What to do to fix cold misfire.

Tiny
WPEDERSON
  • 2004 CADILLAC DEVILLE
  • 78,000 MILES

After sitting for the last month, the engine misfires at cold startup. Misfire evens when put under a load. No hydrocarbons detectible in the coolant. Misfire more severe as weather gets colder. Dealer mechanic pulled one or two plugs which appear to to be fine. Dealer mechanic says the rough cold idle is "normal" but I have driven the car since new and know better. Too, I have rented a number of these cars, including newer, and found that none of them start up with a rough idle. I wonder about fuel air mixture, which would point to the throttle body or the secondary air pump. Are there sensers there that could cause this condition? Other?

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Wednesday, November 9th, 2011 AT 4:58 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
  • 68,398 POSTS

It could be a vacuum leak, the plugs may need replaced even if the couple he pulled look good. If a check engine light has come on, have the computer scanned to identify where the trouble is coming from. And, no, it isn't normal.

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Wednesday, November 9th, 2011 AT 5:23 PM
Tiny
WPEDERSON
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The dealer mechanic states that a check for vacuum leaks was done and there were no leaks.

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Wednesday, November 9th, 2011 AT 6:51 PM
Tiny
JACOBANDNICKOLAS
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That is the most common cause. Has the check engine light come on?

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Wednesday, November 9th, 2011 AT 6:58 PM
Tiny
WPEDERSON
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No, the check engine light has not come on. The mechanic said that an instant read of codes indicated that the car was sending a code (I don't know what that was) but that it was not strong enough to register. Is it possible that one of the in-bank oxygen sensers could cause the secondary air pump to lean out the air-fuel mixture sufficiently to cause this condition? If not, then it seems that the only logical problem is bad spark plugs?

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Wednesday, November 9th, 2011 AT 7:01 PM
Tiny
JACOBANDNICKOLAS
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An O2 sensor can cause a lean mixture. Also, a temp sensor can do the same.

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Wednesday, November 9th, 2011 AT 7:04 PM

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