Cruise Control pulsing problem.

[rg570lvr]

Hope this is the right section for this. My 08 Yaris with automatic tranny came with factory installed cruise control which works properly sometimes. Most of the time when I set it, after a few seconds it starts pulsing the gas like every 2 seconds continuouslly over and over, (kind of like if you set yours to a certain speed and you kept touching the gas pedal with your foot over and over). I've tried setting it at all different speeds from maybe 30 to 70 and it always does it the same. This is on perfectly flat smooth roads with no hills, overpasses or curves to affect the speed, also not in windy conditions. I've brought it into the dealership to get it fixed a few times and they always claim it works fine everytime and they can't fix anthing or change parts without "duplicating the problem". I called Toyota and complained about the problem but they side with the dealership. If I do use it, it can't be good for my gas mileage plus it makes me car sick. I got ticked off one time and asked them "can you refund me the money I paid for the cruise control since I can't use it ?", and they didn't think it was very funny...Any thoughts? Thanks.