Engine Controls - Idle Misfire/DTC's P0171/P0174

SOURCE: Isuzu Service News

TITLE: Cold Engine Misfire at Idle With Possible P0171 and/or P0174

APPLIES TO: 03-05 Ascender 5.3L

SERVICE TIP:

Condition:

5.3L engine may experience any of the following:
1. A cold rough idle that diminishes as the engine warms up.
2. Possible DTCs P0171, P0174, or P0300.
3. Random misfires at idle.

Correction:

Check intake manifold seals around the intake ports for leaks that can cause a lean condition. Intake manifolds can leak around the bottom side of the port, making it a challenge to detect a vacuum leak. Lower than normal MAF readings may mean the seals are leaking around the ports.

1. If leaking intake gasket seals are found, replace the gaskets with updated part number 8-89017-589-0. Updated gaskets (part number 8-89017-589-0) are teal green and replace original orange color.
2. Check intake plenum for excessive warpage that may cause an uneven clamping pressure on the seal. If the plenum is warped it will need to be replaced. Service Information states, "An intake manifold with warpage in excess of 3mm (0.118 in) over a 200mm (7.87 in) area should be replaced". Intake warpage is measured from the gasket sealing surfaces and should be measured within a 200mm (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.