every time i get to about 4000 rpm's my tach starts to just jump up and down, there is no change in the engine, its just the needle and it seems to just happen for the first 10 or 20 minutes i drive the car, after that it goes away.... i had this problem before and all i did was changed the rotor and it went to normal.. but now what can it be??
Thanks

 

This is a sign of your ignitor going bad.

 

you didnt recently clean your engine did you? that happened to mine when i cleaned my engine, the dist. plugs just got wet...dried them and it works fine now

 

Cleaned my engine the other day and the same thing happened. Not only did the tach jump I also had a hesitation/miss at take off. Changed the igniter, all is well now.

 

Happened to my brother. Changed the ignitor, and all is well.