RPM dip while in neutral?

[fuct]

Ok after 3 years of ownership Ive finally made a thread about my RPM's that dip once i put the car in neutral at stop lights.

heres the situation:

car is at normal operating temps. AC is on but not blasting. Weather outside is hot and humid. im driving along like normal and come up to a stop light. i stop at the light and put the car in neutral while i wait for the light to change. as im waiting there my RPM's will dip from the normal 750 to just under 500 and go right back to 750.......

is this normal?

ive recently had my fuel pump changed out after it quit working on me a few months ago. the dipping RPM's happened before and after the fuel pump change so i dont believe it is fuel pump related. during the fuel pump change i also put in a brand new battery. also i cleaned out and re oiled my K&N air filters around that time too. (i made sure not to over oil and i cleaned the MAF sensors with electrical cleaner a week after the filters were cleaned just in case they were dirty)

any one have any ideas?