There's two things to consider. Spark plugs are the logical and most common cause of multiple-cylinder misfires, but since you replaced them already, the fuel supply system is the next suspect. Your engine uses six ignition coils and no spark plug wires. It's highly unlikely six coils would all become weak at the same time. Low fuel pressure can cause lean misfires and idling problems, but the second thing to look at is the idle speed control system.
Your mechanic can connect a scanner to view live data. It won't show fuel pressure but it will show what the Engine Computer is doing with idle speed. You'll be able to determine if the computer is trying to raise idle speed without success, or if it is not trying to raise idle speed. An idle air passage could be blocked with carbon. If additional air can't get in to go with the additional fuel commanded by the computer, you may see some black smoke from the tail pipe, or you may see the exhaust staying too rich too long.
Also look at the intake air temperature sensor's readings to see if it is reporting an accurate air temperature. Temperature sensors have a very low failure rate but connector terminals are noted for loose or corroded connections. The computer uses the air temperature readings to do electronically what a mechanical choke used to do, ... Give the engine more fuel when it is cold.
Sunday, January 12th, 2014 AT 4:38 PM