Your AC compressor may have kicked in. It should not be more than a slight RPM drop, may be 50-100 RPMs at most.
I didn't have my AC on nor the defroster. I read it could be a spark plug problem?
I would look elsewhere. If it was a plug issue, you would also expect to have a distinct miss or stumble, not just a drop in RPM's. Sounds more like a sensor in the engine controls. Have you checked to see if it is throwing any codes?
What would cause the rpm to drop sitting at a light with a whine sound on a 2006 grand prix?
2006 Pontiac Grand Prix GT
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Maintenance & Repair
While driving, when I hit around 55 mph my rpm will suddenly drop down for a split second then resumes as normal. At least that's how it started, then one day while driving my rpm just dropped and...
2006 Pontiac Grand Prix
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Maintenance & Repair
Why does my car sputter hard when i reaches 4 RPM?
2002 Pontiac Grand Prix GT
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Maintenance & Repair
oil pressure dropped to zero while driving and light came on. Car still runs the same. Possible reasons for pressure loss?
2004 Pontiac Grand Prix
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Maintenance & Repair
What could be causing my car to overheat? I have changed the water pump, the thermostat, and the radiator.
1995 Pontiac Grand Prix
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Maintenance & Repair
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