replace them all at once, not piecemeal.

Also, while I am betting you have a 6-cylinder, it would be best if you put your X's details in your signature. Helps with troubleshooting.

__________________
Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual