The tachometer in the car is very erratic.Sometimes the needle doesn't move when you start the engine, other times it goes a way highin winter it would go all the way around,sometimes it reads right.

More than likely the tachometer is defective, the little motor that moves the needle is failing, this is called the "Stepper Motor" The cluster can be repaired, check online for repair sites, cost around $200.00 US

Tachometer / Speedometer Problems: - Ford Explorer and Ranger ...

www.explorerforum.com > ... > Under the Hood

Jul 31, 2006 - 13 posts - ‎11 authors
Tachometer / Speedometer Problems: Under the Hood. ... upon restat the speedo goesto (is driven to) zero, the tach goes to ... 88 89 93 95 96 Aerostars ... in cold weather it seems to stick. but once the truck's interior warms up, .... 1995 Ford Explorer 4.0Automatic My Tach Quit Working And So Did My ... 5R55S harsh shifting; bump engaging reverse;
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1999 Ford Explorer , Erratic RPM Problem - YouTube

You have a engine RPM sensor that is not working correctly. Computer thinks you have push gas pedal to the floor and is providing that type of shift. It may be the sensor attached to your gas pedal has worn out.

yes it could be

Hello ,
it could be a crankshaft sensor being the tac needle
is acting this way.

Hi there:
Possible ground wire fault with dash board unit. If it is a cable operated spedo, the cable end (small square cap) may be rounding off on one end.



Check the plug at the cluster, if it is ok then travel to your nearest GM dealer and ask them to see if there is a software update addressing your issue.



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sounds like a computer reset problem

First thing that comes to mind is leaking o-rings at the injectors-does it act like it is flooded, like it wants to start?

If it sounds like it doesn't want to start at all (just cranks) check the crank sensor-it may be failing and when it gets hot, it has too much resistance to fire the ignition. Observe the tachometer when cranking the engine, if the needle is not moving, it is the crank sensor.

when the engine is cold all the fluids in the engine are "cold" and it is a little thicker than it is when it is warm so just start it a little earlier than you normaly would to give it all time to get warm, another benifit to this is no cold car to climb into.

2005 BUICK LESABRE TACHOMETER DOES NOT REGISTER WHEN ENGINE IS RUNNING. SOMETIMES IT BARELY MOVES, THEN GOES BACK TO 0
SAME CAR HAD SPEEDOMETER QUIT, REPLACED WITH NEW SENSOR, DROVE ABOUT 1300 MILES AND IT QUIT AGAIN. CLEANED THE SENSOR, WORKS OK NOW.