Speedo doing 20 at idle?

[HIGHFIV5]

I searched like mad but couldnt really find anything quite like my problem.I have an 89 and first off it usually idles around 1300 RPMS.Pre sure thats just a vacuum leak which i have yet to find but also upon idlethe speedo says im doin 20km/h and when i rev it up the speedo movesup as well. Although ive noticed if i drive it for a bit the idle usually calms down to750 and the speedo doesnt do anything crazy. But ive only had it out like twicecause my rear calipers are seized atm so shes not on the road quite yet.And on that note...im having a really hard time deciding the route i shouldgo with the rear brakes?The Q45 setup sounds ridiculous to make the parking brake work.And the 300ZX setup would need the master cylinder,but i could get easy park brake cables from PDM.Anyone know of any other cost effective and just overall great upgrades i can do for mah rear brakes?I wanna get mah baby on the road!!Any ideas?

THANKS!!!