I just solved my car from slamming into gear due to high idle. I replaced the idle control valve. I think also if that is not it a bad OVP can cause a high idle, but if the car starts easily when cold, thats probably not the issue.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual