When the Griffins are standing on Quagmire's front porch, their house can be seen next door in the background even though it was supposed to have disappeared as a result of the poltergeist.
When Lois and Stewie escape the spirit world, via Meg, they were covered in a pinkish kind of goo. However, when they ran out of the house and into the car, the goo was gone.
When Lois goes in looking for Stewie, Peter ties a rope around her so they don't lose her, but when she finds Stewie and they exit out of Meg's ass, Lois has no rope around her.
When the Poltergeist stacks the chairs and refrigerator the handles on the fridge are on the wrong side.
In the scene where Adam West is talking with the girl from the Home Improvement store, the sign in the back says "No Tresspassing". Trespassing is spelled incorrectly.