Rough Idle or Misfire on 2002-04 GM 5.3L VIN Z Engines
The L59 engine is calibrated for ethanol fuel (E85). Due to the low volatility of ethanol, the PCM provides higher fuel flow through the injector, which may pool on the upper manifold to head gasket material. Over time (usually 12 months and longer), the gasket material may degrade resulting in an unmetered air leak.
To correct this problem, GM states that you need to replace the upper intake gaskets with the teal green gasket material (P/N 89017589). Important: Do not replace the upper intake manifold gaskets with the original orange gasket material (P/N 17113557).
- Locate a straight edge across the intake manifold cylinder head deck surface. Position the straight edge across two runner port openings.
- Insert a feeler gauge between the intake manifold and the straight edge. An intake manifold with warpage in excess of .118” (3mm) over a 7.870” (200mm) area is warped and should be replaced. Do not replace intake manifolds with warpage that measures less than .118” (3mm) over a 7.870” (200mm).