On my brother's 89 3 door, the tach needle jumps around. Am I right in the assumption the distributor is going out?

 

What else could it be?

Yup... thats a classic sign that the disty is on its way south.

 

-Brian

More precisely, the bushings in the distributor are shot - they can be replaced cheaply.

 

GD

Check for play in the distributor shaft; if none, check wiring to coil and sparkplugs. Normally, this is due to the distributor bushings having too much play as GD already pointed out.

Don't forget to check for loose wires first.