been having an issue with my x350 and i think its going to get worse am pretty sure its a power issue and would like some advice on what it could be

driving home yesterday i slowed down at lights and the car cuts out restarted it and everything has been fine it has not done it since but i think its going to get worse any idea what could of caused this?

ive noticed when i use the climate control or any of the toys my main lights will dim also if i use the power steering when idle the rev gauge will drop is this normal?

it had other power problems a few months back turned out to be the earth points which where relocated and seem to have fixed the problem but now am getting these new issues. i have replaced the battery with a brand new one and checked the alternator which seemed to be fine.

any help with this would be great thanks.

 

Could be any of quite a few but one that's easy to check for is an air leak - use OBD live data to look at fuel trims.