I have a 2003 Honda Civic EX. It has a D17A2 with a 4-speed auto transmission. I have noticed the car will idle at 10 psi when in gear, but as soon as I put it into park it drops to about 7 psi and almost immediately returns to 10 psi. If I leave it in park without touching throttle, the oil pressure will hold steady at 10 psi, but every 2-3 minutes it will drop to 7 or 8 psi for a second and then go right back to 10 psi. Engine RPM drops about 100-200 rpm as well when this happens.

172000 on chassis
105000 on motor (timing belt/oil pump/water pump service was done 40000 miles ago)
Spark plugs were replaced 10,000 miles ago
The car does have a ram intake so I checked for vacuum leaks and found nothing.
IAC is set to 750 rpm when warm
I notice no loss of power or lugging of the engine, so ignition coils must be fine, right?
Oil level is fine and its changed every 3500 miles along with the filter

It could be that the car is just old, but if this oil pressure scenario can be fixed I would like to know what you think it could be since it is driving me crazy!

Thanks in advance!