OIL ( again )

I've always used 10W30 oil in my BUICK 3.1 engine.
This last change, they put in Mobil 5W30.
I swear, the engine idles faster !
Could a minor change in oil weight
make enough difference to change idle speed ? Did it reduce that much friction ?
( or should I look for a hose that got knocked loose ? )
<rj>
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The computer controls the idle speed on a 3.1, not internal friction or lack of it, syn oil can reduce this friction as well as the lighter weight oil.

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