Hi tpros,
i think we have the same damn problem!! have you also noted that when your car is first started in the morning the power is there until the car warms up?!
here is a youtube vid of my 500 'pulsing' at constant speed...i cant believe 2000views and no one knows the exact problem
http://au.youtube.com/watch?v=eiwKaI5Y1eE&feature=channel_page
if you find a proper fix, please let me know
nathan