Check this out... the basis for my theory above:
Service Bulletin
File In Section: 06 - Engine/Propulsion System Bulletin No.: 04-06-04-078 Date: October, 2004
TECHNICAL
Subject: Hesitation, Roughness, Light Chuggle or Check Engine Light, DTC P0300 (Reprogram PCM)
Models: 2004-05 Pontiac Grand Prix
with 3.8L Engine (VIN 4 - RPO L32)
Condition
Some customers may comment on a hesitation or engine roughness with or without the Check Engine Light illuminating. Upon investigation, the technician may or may not find code P0300, Random Misfire Detected. In some rare cases, the customer may comment on a light surge or fishbite when crowding the throttle with the TCC applied.
Correction
if a DTC code P0300 is set, follow the diagnostics in the appropriate Service Manual. If the diagnostics do not lead to a solution or if no DTC code is set, then reprogram the PCM. A new calibration has been released to address this concern. The following tables show the calibration number for reference, program the PCM with the appropriate listed calibration, or later, for this condition.
