2004 Chevy Tahoe Rough Idle, engine light on

I worry when 2 cylinders next to each other misfire, can be a head gasket, or cracked head, can also be the injector harness connectors are crossed at thos cyls...compression test , and wire check! Also if it's Flex fuel vehicle, there is a TSB on intake manifold gasket, read it below.

Flexible Fuel (RPO L59) Rough Idle, Misfire, MIL DTC P0300 (Install Intake Manifold Gaskets With Teal Green Gasket Material) TECHNICAL SERVICE BULLETIN Reference Number(s): 05-06-04-029A, Â Date of Issue: Â June 24, 2005 Related Ref Number(s): 05-06-04-029A ARTICLE BEGINNING SERVICE INFORMATION 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. Over time (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. Inspect Intake Manifold to Cylinder head Deck for Warpage Affected Model(s): 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). Supercedes: 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. IMPORTANT: Do not replace the upper intake manifold gaskets with the original orange gasket material, P/N 17113557.Fig. 1: Intake Manifold Courtesy of GENERAL MOTORS CORP. 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). PARTS INFORMATION Parts Information WARRANTY INFORMATION For vehicles repaired under warranty, use: Warranty Information Part Number Description 89017589 Gaskets, Upper Intake Manifold (Teal Green) Labor Operation Description Labor Time J 0251 Gasket, Intake Manifold - Replace Use Published Labor Operation Time

Check for that vacuum leak, even if you havent run E85 in it, it's the volume of the fuel that matters. Could be the gasket at the intake still, a compression test especiallt at 4-6 will tell you if it's more severe, if the compression at those 2 cyls, is the same as the others, the heads, valves and pistons are good. Spray around the intake with throttle body cleaner, when the idle changes, you have found a leak. Also the fuel injectors may be dirty, try cleaning and testing the ohms, use a noid light to see if the harness is powering them up.