What kind of low rpm are you talking about? Do you mean in gear around idle? That would just be the engine trying to drag the car along at a way lower than intended engine speed.
If it is happening at a normal cruising rpm while on steady throttle, that could be a problem with the emissions controls or a clogged IAC.
First thing is first, go over all the plugs and wire and make sure everything is tight. Simple things can present as big problems sometimes.
-Tim
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