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?
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.
November, 9, 2011 AT 6:51 PM
The dealer mechanic states that a check for vacuum leaks was done and there were no leaks.
November, 9, 2011 AT 6:58 PM
That is the most common cause. Has the check engine light come on?
November, 9, 2011 AT 7:01 PM
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?
November, 9, 2011 AT 7:04 PM
An O2 sensor can cause a lean mixture. Also, a temp sensor can do the same.