RPMs won't drop

[Supermini]

Alright it's a 2000 3.0 manual. intermittently it will hold the RPMs up way high between shifts or coming to a stop with the clutch in and won't drop down until i come close to a stop and even then sometimes idles high for around 10-20 seconds. if i shift around 2000 RPMs, when i put the clutch in it will sometimes rev up to close to 3000 in the time it takes me to shift, not really aggressively but it climbs up there and pretty much stays til the clutch comes back out. I've had this problem before and replaced the idle air control on a hunch but no change. Ive got a autometer vac gauge and when it's causing the problem it's around 15lbs as opposed to 17-18 when running normally. What would be causing this?

 

[basketranger]

sounds like an old fashioned vacuum leak. dont forget to check or maybe change the brake booster vacuum line.