Always replace that washer. when it's been reused, the correct amount of torque will sometime not effect a good seal. Designed to be crushed once and once only. There are a number of things that can cause low idle speed. You should get a run on a computer to firm it up.
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.