2003 Chevy Tahoe Rought Idle with P0171 and P0174 OBC codes

OTTONUILA

MEMBER
2003 CHEVROLET TAHOE
V8
4WD
AUTOMATIC
113,000 MILES

I have changed the 4 oxygen sensor, the fuel filter, the 8 sparkplugs and wires and the PCV and run 2 cans of sea foam for the injectors, new air filter, and oil change and cleaned the MAF but still get the error codes. I also donated $10 to 2CarPro. What should I try next. The car runs great accelerating and cruising but Idle is cycle rough idle with the P0171 and P0174 OBC codes and the check engine light on. I cannot pass emissions. What should I try next. Thanks

1 Reply

BRIAN 1

MECHANIC
1,030 POSTS

You could try cleaning the injectors at the fuel rail or follow this bulletin.99 through 05 GEN III truck engines may experience any of the following:

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.
The intake plenum should also be checked for excessive warpage that may cause an uneven clamping pressure of the seal. If the plenum is found to be warped it will need to be replaced. Service Information states, "An intake manifold with warpage in excess of 3 mm (0.118 in) over a 200 mm (7.87 in) area should be replaced". Intake warpage is measured at the gasket sealing surfaces, and should be measured within a 200 mm (7.87 in) area. This measurement is across only two of the intake runner port openings. Measurements taken across the entire distance of all four intake runner ports will lead to unnecessary manifold replacements. Try these suggestions.