RPM gauge on o3 trailblazer

[bassman186]

can someone give me advice on this problem.

2003 trailblazer v6 vortec

rpm guage will be at 7000 rpms when only going 20 mph or it may be at 5000 when idling & 4000 rps when engine is shut off.

the guage will sometimes jump back & forth but no difference in way engine runs,engine runs good as it did when rpm gauge was working correct.

no problem with engine at all.will set all day & rpm is still at 4000 to 5000 thanks for any advice.

[jeffreyd]

it think it picks up the rpm out of the altenator. could have a wire that is bad or ground. have you done any engine worek recently

[Jeremy airjer W]

What happens if you cycle the key. Turn it on without starting the vehicle (run position) then turn it off. Repeat a couple of times. Does the tach fall from its current position.