tach jumping

[deathegg]

Hey everyone,
I just noticed that my tachometer (not stock, an aftermarket one),
sometimes will "jump" or "twich" when at idle. Nothing big, just 100-200 rpm.
The engine itself is not doing it, it is a steady idle speed when this is happening. Just the tach needle is a little jumpy.
I thought that perhaps the coil is bad since that's where it gets its signal?
Any thoughts??
Thanks!
Mark

[sasquatch]

is it a good tach? my freind bought a junk one for like 20 bucks and it started acting up last week.

[jglutz]

Does your aftermarket tach have a confuration switch....4 - 6 - 8 cylinder? If so make sure the switch is not between positions or move it to another postion and see if the problem goes away. Also, check the tach ground.

If your coil was going bad...you should have noticed more than just the tach jump...you would hear idle changes and experience performance problems.