I have a gauge dial on the dash which indicates RPM X 1000 on my 2002 Acura MDX. The pointer normally pointed to 2 when the engine was running. I have recently noticed that it points to 1 or lower when the engine is running, though it jumps to 2 and over when I press the gas pedal or accelerate and quickly falls back to 1. The car runs fine, but at lower speeds I feel the engine vibrate once in a while. What does this indicate. Appreciate your guidance.