High Idle on Cold Start/Stalling on Hot Start

Hello,

I am having both persistent and intermittent problems on my 2000 Honda Accord V6. The car will idle very high on a cold start and will suffer from serious power loss until it warms up. This problem occurs whenever the car has been sitting for a long period of time. It will also occasionally stall on a hot start. It will start fine, but will not hold the idle in Park. Lately, I have noticed the idle getting rough whenever it is in Park. The following things have been done to try to address this: new coolant temp sensor, new throttle body with all related sensors, new fuel pressure regulator. Both problems continue. The car does have an aftermarket K&N air intake. My private mechanic and the dealer are both stumped.

Any ideas?

Thanks!