My tach. is bouncing all over the place when driving ,it looks like the needle is struggling to move up.Even when the clutch is diengaged,and i'm just coasting the needle will bounce all the way down to idle.

Any suggestions ,what would cause the tach to do that?

I already replaced the icm,tps,iac,plugs.I was wondering if it was the cluster ,or the computer?

Thanks for the help in advance!!!!!!!!!!!