Any engine codes?

My guess is the stepper motor in the dash for the tach. If you have a scan tool you can try and see what the ECM is seeing and if it is steady. Does the engines have a higher cold idle and then reduce as the engine warms up? It sounds like the engine is perfect but the tach is not for the 1st 20 sec.

 

No codes no other issue (other then airbag light). Warm up is normal once bounce settles, warms at 1600ish idle between 800 to 1k from what I've paid attention too. I only hit 2 stop sign and 2 lights before I'm on a 65mph highway and at 530 before my coffee is 1/2 gone I'm not really paying the closest attention

 

But just to clarify..............The engines RPMs sound normal (ignoring the tach and lack of caffine) while the tach does it's 20 sec bouncing thing? The engine doesn't rev to 5K (using your ear) and back and bounce up and down with the tach correct?

 

Correct, motor runs normal, no hesitation, ect. I consider it a mild inconvenience.

 

Was your car covered under the ECU recall from many years ago? Sounds strongly like an ECU issue or a loose connection or a bad ground. Does your temp gauge work as it should? Do any recent electrical work on the car? Install any LED bulbs? Does your AC work when the RPM jumps? I know you said it had no codes, does that mean pending codes as well?

 

Haven't hooked a code reader up. No idea about ecu (purchased car July 3rd this year). Temp gauge works fine. A.C. cycles fine (defroster). The rpms don't actually change at all its just the gauge. Leds in tail lights, hvac controls. Stock lights in cluster. No electrical changes done for at least a month before this started.

 

You are right it is a minor inconvenience. If the ECU checks out ok I suspect the tach in the cluster.

FYI (not a corolla):

Tachometer Bouncing Issue/ECU - info

I didn't find much here regarding this, but resolved it yesterday and thought I'd share the info: I've got a 2007 LE Automatic @ 78K miles. The tach began bouncing weeks ago, then the Check Engine light came on (not at the same time). The actual RPM's did not change physically, so I thought...

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