I recently brought my car back to life after a sleep of several months.

In the past, the tach behaved it's self normally.

I had taken the instrument panel out in the past to take care of the speedo issues.

The tach behaves it's self some of the time, but generally is pegged at 8500 at normal speeds in town. Sometimes the needle dances between 4000 to 8500 at idle. The engine itself is quiet, as it should be at idle.

So how do I go about taking care of this?

 

Youtube shows rev the engine fast 3-4k, you may reset the position of the needle to normal position. Or else ...

1999 EL-FSM shows diagram and test procedure. Basically, tach is a stepper motor that its shaft is calibrated to rotate at certain angle depending on signal voltage.

From the image, tach receives rpm signal from ECM through BR(own) connector at pin 17, ground is provided through pin 31. The tach is powered through W(hite) connector at pin 41.

The FSM test is below especially the 3rd one is applicable to your case:
- Key on, connector is plugged in, test for 12V DC at pin 41.
- Key off, connector unplugged, test for continuity to ground, pin 31.
- Start car, connector unplugged, test for signal between pin 17 and 31.

Or, you may connect an external tach to see if rpm signal is stable.

Just for luck, you may inspect the printed circuit, tracing the connector pin 17, or pin 31 to tach for any corroded connection/solder points.

 

Great info saig! Thanks!

 

Thank you.

I will trace this down soon.

 

No problem, hope it make sense .

 

my tach hasn't worked in 8 years . Don't need it