B18C1 Reving up and down at idle?

Ok the motor is stock and at ide it revs up and down over and over again. Idk Why but its not low on coolent, no check engine light , no vacum leaks, idk, And Another thing its only redlining at 6,800 rpm when it should be 8,000rpm?? Please Help Can Even Text me 937 733 6232 thnks