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one thing people overlook is presure testing the exhaust sytem with boost leak tester as a leak pre turbo not only hurts spool up greatly and makes your car feel so much less performance but also is one of the most common reasons for lean idle/misfire at idle (intake side vacuum leak is most common)
if you have lean idle and it goes away when you give it any throttle and cant find a boost leak on intake side throw the tester on exhaust and see if you have pre o2 sensor leak. this was a issue i had where car misfires at idle and the fix was the manifold to turbo gasket.i was seeing 18+ afr at idle where it would begin to stumble.
the theory here is simple.at a certain duration your engine not only pushes out air but pulses from cam timing,if you have a leak pre o2 sensor each pulse every rotation will draw in fresh unmetered air before the o2 sensor,this causes the lean idle.as you rev up the engine your increasing the exhaut flow more and will see your lean condition go away.
it will look just like a vacuum leak since engines see the most vacuum at idle and less vacuum the more you open the throttle this also causes lean at idle and gets normal as you hit throttle since your drawing in more unmetered air past the o2 at idle and vacuum stabalizes the more you open that throttle.
i wanted to add this because the symptoms felt identical to a vacuum leak and it seems like somthing grossly overlooked to the point people think sr is supposed to idle lean,it should idle close to stoich (14.7 not 16-17 or more.)
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