I'm having an issue with my tach lately.
Whenever idling in gear or in park, the tach reads unusually low. After a few seconds, it will eventually bottom out at the 0 peg and stay there. However, it may jump to ~500RPM and fall again to 0 shortly repeating this cycle as long as the engine remains idling.

The engine is not idling as low as the tach is reading. I have verified from my ScanGauge a normal RPM of ~800 in Park.

When the engine speed is raised above idle, the tach seems to function normally and read similar to the ScanGauge.

There are no CEL codes.

Any suggestions?

 

Not good.. Since the PCM is seeing it accurately it's most likely the guage cluster.

On *other* engines, I've seen the tach jump because of loose wire on plug connections and because of bad ignition modules.

Rich

 

Oh, i read it as "erotic tachometer" my bad

 

I'm having the same problem with my 01 ranger.. Did you get it fixed?

 

My truck is doing the same thing, I have fixed it once.

There is a bad contact for the tach, its on the cluster where the connector plugs in. The thin copper has developed a bit of corrosion, probably form it being touched.