I have a 1999 Maxima GXE manual. Its been having some weird idle characteristics lately. When I push in the clutch to down shift, or if I am coming to a stop, it will drop the rpms down so low that that car starts to rough idle (250-350 rpm). What controls this dropping down so low? Would this be vacuum? Is it part of the throttle cable connection? Please, all info you can give me on this I would appreciate it.

 

In my experience a half-clogged fuel filter is at fault.

There are other possible reasons, but that's a biggie. If you also notice the tranny grinds or is hard to shift, it may be due to clutch problems.