Zthirty4NISMO

Mother in law has an 03 Pontiac Bonneville with the naturally aspirated 3.8l. Car has a condition where it does not idle well in park and will sometimes stall. I diagnosed bad MAP and MAF sensors and replaced both of those. The problem still exists but seems better. I also did the idle air control motor for the heck of it but still nothing. The car seems fine during normal driving and also idles good when at a stop in drive. Shifting from any gear to park is the worst. When going into park the rpms will surge and dip very low to the point where most of the time it stalls. Before replacing some of those parts I had to worry about it stalling in stop and go traffic but I haven't had that happen yet again.

Does anyone have ideas? It has about 165k miles and do not know the tune up history or any repair details. Thanks

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