What would make a 2004 Mini Cooper S surge?

Answer 1

I have a 2004 Mini Cooper S JCW edition and last year the power steering pump failed. I replaced the Power Steering pump with one from auto zone (let's face it, BMW is way too expensive) and every since then the car has literally pulsed. It's like there is a drain on the battery (but that was checked and it's fine) because the car "surges" rhythmically and if the lights or the heat is on, the lights will dim every few seconds and the heat will be full blast then almost stop and then go back to full blast. And it's constant, it's done it since the original power steering pump failed. I took the car to a mini mechanic and they told me they don't know what is wrong with the car. Seriously? And it is gradually getting worse and makes me worry that it is something that could do a lot of damage to the car. It also runs hotter than usual and the mpg is not as good as before. So do you know what could be making my car do this? Thanks