RPM needle problem!!!!!!!!!!!!!

[e30 ram0s]

so its not my crank pos. sensor. in the cold cold morning, my rpm needle rev's up ever-so-smoothly but later in the afternoon where everything is has warmed up, my rpm needle glitches. why

[92 mtechnic cabrio]

it's a tachometer.

and check the brass fittings behind the cluster. make sure they're all tight, like tight tight.