Evert time I start my mustang the rmp are so high for a couple seconds sounds like I have my foot all the way down on pedal and my belt screeches but it only lasts couple seconds and its gone
Updated 26-Oct-2019 to clarify creeping idle RPM increase as the car is being driven. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of...
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Start at the top and go step by step, don't skip around, even if replaced or worked in that area already. The next step depends on the result from the one before.
Can't give you a definite 'do this or that' with the limited info given and even if I could it would be just guessing and may lead to wasting time and money.