I have recently purchased an E150 Custom Van with only 4500 miles on it .It has a 4.6 v8 engine which when first started hot or cold will race up to over 1500 rpm and then reduce to about 800rpm and runs well. I am trying to determine how this startup rpm can be adjusted.(I have a good background on anything with a carb. on it but the newer injected engines ,need some help.) Thank you.