I have had this problem off and on, I thought it may be ECU or Grounding issues. The installation of the megasquirt and cleaning up grounds didnt work. Although I only cleaned the one by the alt/throttle body, and the one under the brakebooster. Anywho, the tach jumps around alot in light throttle and idle. When you hit boost, the damn thing pulls fine. I can't figure out what is causing this. I still have cam angle sensor and stock coils. This causes a miss at low speeds and cruising and my car bucks and sputters alot while trying to drive through parking spots and low speed sections, Here is a video too.
Sorry, I took it on my phone, I know it looks like I am in neutral and revving it, but I am just cruising in 3rd and my tach is just doing it's thing.
I once had bad plugs that caused one hell of a misfire (though under boost) and the tach would dither about when the condition occurred. Did you remove/refresh the enngine-to-body ground strap? Might try that as well. You tach bouncing isn't causing a misfire...some issue is causing a misfire and your tach is bouncing around because of it.