Why is there strong suction if I try to pull off oil fill cap while car is idling

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! The strong suction at your Lucerne’s oil fill cap is likely due to excessive crankcase vacuum, which points to a possible problem with the PCV (positive crankcase ventilation) system. If the PCV valve is stuck open or malfunctioning, it can create too much vacuum, which explains the suction and even the blue smoke (from oil being pulled into the intake). The chirping sound is likely from air being sucked through small leaks or gaskets, and it stops when you relieve the vacuum by pulling the dipstick. You’ll want to get that PCV system checked out before it leads to more damage. If you need any further advice or if you'd like help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554!