I have found the MAF sensor can cause these problems and the MAF is a normal maintenance item if you have not installed a new one recently I would give that a try.
Here is a guide.
Here is some book wisdom.
A cold rough idle that diminishes as the engine warms up.
Possible DTCS P0171, P0174, or P0300.
Random misfires at idle.
The intake gasket seals may be leaking around the intake ports, causing a lean condition. The intake gasket seals may leak around the bottom side of the port, making it a challenge to detect the vacuum leak. The technician may also notice lower than normal MAF readings if the intake seals are leaking.
If leaking intake gasket seals are found, replace the intake gaskets. During the repair be sure to use the current GMSPO part number for replacement intake gaskets. The current GMSPO part number for intake gaskets will have a teal green intake gasket seal. The old version of the intake gaskets were orange in color. Use only the teal green colored gaskets for a repair.
Check for vacuum leaks again you might find a problem.
please post back with what you find.
Tuesday, December 16th, 2008 AT 1:16 PM