Take a look at throttle opening percentage / voltage at idle.
If the numbers are low, it points towards a vacuum leak post throttle body because the throttle is closing to maintain idle speed. A failing brake booster can cause a vacuum leak also.
If the throttle numbers are normal and MAF low, you have air entering between the MAF and throttle body ( maybe from the crank case breather through a oil cap / dipstick o ring ).
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