2006 XLT engine stumbles on P and N gear

[kevinlu]

Just bought this 2006 expedition XLT with about 120k miles. It's a 2wd, automatic transmission. Looks previous owner took good care of it. It runs and drives good. Engine runs and feels smooth on D, R, 2 and 1. But when on P and N, engine stumbles a little bit at a frequency of about once every 2 seconds. Not that bad, but I can feel it on driver's seat. After open the hood, I can see the engine rocks a little bit when it is at P or N. No "check engine" light. No other issues so far. Any clue what might be wrong, or maybe it's just normal? Thanks in advance!

 

[r stRratus]

I have the same year and model, having similar situation. Some say that maybe mass air flow sensor needs to be cleaned, I'll be doing that in a few days to see if that relieves the problem, doesn't hurt to check it out...