2007 Mini Cooper S R56 - low / no power at startup
 

I own a 2007 R56 Mini Cooper S: when started it won't rev up right away, mainly the first time driven each day. I takes a minute or two to warm up and then on occasion backfire (one or two pops) when slowing on 3rd gear mainly. Biggest risk is to have it stall or loss of power when entering traffic.

I've replaced the vacuum pump and wastegate recently and had a local mini shop tune the wastegate but still no success with the sluggishness and back fire. The shop told me the also "smoke" tested all my vac lines for leaks.

Any advice or troubleshooting techniques would be appreciated.