High idle in park can be caused by a variety of factors. A few common causes include dirty or clogged fuel injectors, air leaks in the intake manifold, vacuum leaks, a faulty throttle position sensor (TPS), and/or an improperly adjusted idle speed control valve. The first step to diagnose high idle in park is to check for any potential air leaks as these can cause an increase in engine RPMs when the vehicle is parked. If no air leak is found then it's time to inspect the throttle position sensor and its related components such as wiring harnesses and connectors for any damage or corrosion that may lead to improper TPS readings. In some cases, adjusting the IACV or Idle Air Control Valve may also help reduce engine idle speeds while parked. Additionally, checking fuel pressure levels and replacing clogged fuel filters are often necessary when dealing with high idles in park as well since they will directly affect how much gasoline is being delivered into the combustion chamber at all times which could further contribute to elevated RPMs when not driving.