My 99 Saturn SL1 does the same RPM hike when clutch is pressed in or shifting to neutral. I've found that it's ECU and IAC related. Disconnecting the battery overnight has fixed that problem, but it seems to be coming back after about a week. Since i do a lot of pulsing between 1800-2300rpm and EOC gliding, i think the ECU is thinking that i don't know how to drive and is trying to hike the rpms to compensate for early shifting?
I suppose, like others have said, putting the IAC on a switch could solve the problem. Or, just disconnecting the IAC all together and manually adjusting the idle speed. I'm going to look in to it further as I,too, feel like it is hindering my fuel economy.
I really like the mods you did to your front end. It looks very clean. All i have right now is clear window seal tape blocking the radiator
. I've been hitting between 43-46mpg this winter, and hope to break 50mpg once the temp warms up here.