tach jumps, 95 Miata wont run at idle ,bought not running, chain towed, key on

What is your question?

bought used not running, bought many used parts, was at shop for four months,not fixed, now home, jacked up rear, started, it shudders in drive, is there a trainy problem ,sensor contributing to my woes too? will search for ground, original comp , did state something about trainy