Tachometer Oscillations

#1
Hi

I have a 2006 Corolla CE (1.8 L). The tachometer oscillates when I start the car in the morning. I turn the ignition off and power on the car after few minutes with my key turned on. This time the oscillations stop and car just works fine without any issues. This issue repeats if I start the car after a long gap.

If I start the car by putting in the key, turning to on position, not cranking it for 3 - 4 minutes and then crank it, the car starts just fine. There are no oscillations (however, I have observed once :( )

I do not hear any whisling sound under the car hood (when Tachometer oscillates) and assume that there are no leaks at the RPM sensor.


Am looking for directions on where the issue might be. Appreciate if anyone could provide clues on what might be happenning and probable solution

Thanks
 
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