I have owned my 2004 since new. The only thing ever done to the car besides maintenance is KN filters. I have aprox 35k on the car, and it has been very reliable and a joy to own. Lately when i start the car, warm or cold, it revs at 1000 rpm, holds at that for a few seconds, and then gradually drops to 600. IF it was only on start up it wouldnt concern me. It occurs even after driving it for 30 minutes. Has anyone had this issue or can recommend a fix. The car had a tuneup aprox 4k ago (spring 2018), wire and plugs. Thanks for any advice