Q: Engine revs up and down when in park and sometimes in drive/reverse; have replaced IAC valve, and the map sensor 1998 Honda Prelude

Hi there - the P0505 code you are getting indicates a problem with the idle air control circuitry. Since you have replaced the IAC valve, this could still be a problem with the connectors or wiring to the IAC. There is a specific "re-learn" process to be performed after installing a new IAC as well - perhaps this was not done, or done correctly? There are also other items that can lead to rough idling: dirty or malfunctioning throttle body or throttle position switch, or air leaks in the intake. I recommend a rough idle inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.