Hi All
On my 2005 Mazda Tribute, my idle speed would rev to about 2000 rpm while decelerating then momentarily drop to under 500 rpm. I have to keep my clutch in so the vehicle would not stall. I have already had the IAC valve replaced, but it hasn't resolved the issue. Complete tune-up also done.

Any assistance would be appreciated.

 

I would check/replace the TPS (cheap part). Then remove the bellows in front of the throttle plate and, using a soft toothbrush and fuel injection system cleaner, spray and lightly scrub around the area where the plate closes (open the plate fully to do this)to remove any buildup. Do not use a solvent as there is a coating on the throttle body. Check all your electrical plugs are tight when reinstalling.

 

How does a manual transmission do that?

 

Sounds like a vacuum leak. Check the line to the EGR valve and along the back of the engine where there are 1/2 a dozen connections. There's a plastic heat shield you will have to roll off to check the connections. Is there an engine light on?