lil help?

my friend has a 1991 crx with a 1990 jdm b16a. he recently made some minor adjustments to his clutch and cut an inch or so off of his intake piping. the problem is that now, between shifts, his rpms fall very rapidly, which they never used to do. he can't even chirp 3rd anymore cuz of it. anyone have any ideas as to what's going on?

did he remove the hose that goes from the intake manifold into the intake piping or move it?

no, it's still where it always was.