I remember this type of concern on cold starts. There is a service bulletin for the intake manifold gasket. This type of concern I would install OE gaskets. When cold it has a lean misfire. Once the engine warms up the gasket expands and seals the vacuum leak. Here is the bulletin.
2002 Chevy Truck C 1500 Truck 2WD
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V8-4.8L VIN V
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Engine - Rough Idle/Misfire/MIL ON/DTC P0300
Vehicle Powertrain Management Technical Service Bulletins Engine - Rough Idle/Misfire/MIL ON/DTC P0300
ENGINE - ROUGH IDLE/MISFIRE/MIL ON/DTC P0300
Bulletin No: 05-06-04-029A
Date: June 24, 2005
TECHNICAL
Subject:
Flexible Fuel (RPO L59) Rough Idle, Misfire, Â MILÂ DTC P0300
(Install Intake Manifold Gaskets With Teal Green Gasket Material)
Models:
2002-2004 Chevrolet Silverado, Suburban, Tahoe
2002-2004 GMC Sierra, Yukon, Yukon XL
with 5.3L Engine and Flexible Fuel (VIN Z - RPO L59)
This bulletin may apply to the following engines using regular fuel: 4.8L, 5.3L, 6.0L (VINs V, T, P, U, N - RPOs LR4, LM7, LM4, LQ4, LQ9).
Supercede:
This bulletin is being revised to add additional diagnostic information. Please discard Corporate Bulletin Number 05-06-04-029 (Section 06 - Engine/Propulsion System).
Important:
  Always begin your diagnosis with the Diagnostic System Check - Engine Controls (SI Document ID # 1289827) for any MIL or driveability concern. The Diagnostic System Check directs you to the next logical step in your diagnosis. Follow the instructions in this bulletin should the rough idle, misfire, or DTC P0300 diagnostic procedure point to an air leak in the intake manifold gasket. Following the published diagnostic procedures will improve diagnostic accuracy and support our fix it right the first time approach.
Condition
Some customers may comment that the vehicle may have a rough idle, misfires and/or a MIL illuminated with a stored DTC P0300.
Cause
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. Overtime (usually 12 months and longer), the gasket material may degrade resulting in an unmetered air leak.
Correction
Replace the upper intake manifold 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.
Inspect Intake Manifold to Cylinder head Deck for Warpage
Important:
  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.
Important:
  Measurements taken across the entire distance of all four intake runner ports will lead to unnecessary intake manifold replacements.
1.  Locate a straight edge across the intake manifold cylinder head deck surface. Position the straight edge across two runner port openings.
2.  Insert a feeler gauge between the intake manifold and the straight edge. An intake manifold with warpage in excess of 3 mm (0.118 in) over a 200 mm (7.87 in) area is warped and should be replaced. Do not replace intake manifolds with warpage that measures less than 3 mm (0.118 in) over a 200 mm (7.87 in).
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Saturday, February 15th, 2020 AT 12:45 AM
