What would cause the tach to go to zero with the engine still running
then go all the way up and down. It's not in tune with the actual rpm
of the engine. Is this a expensive problem?

It is probably a loose wire on the distributor pickup. I am not totally
familiar with the mustang tach system but had a similar problem with a
Fiero. the wire was actually burned through and would short out.

<landsteam (AT) yahoo (DOT) com> wrote