the "d" light (in the gear lights panel) starts blinking sometimes. i had it checked at city sales and they say the countershaft speed sensor is faulty. i also noticed a jerk when the car shifts from first to second gear (prosmatec), the sjerk is reduced if the ac is switched off. could someone explain to me whats going on?? i recently had landi renzo gas installed...could that be the reason?? any ideas??