I addressed this in another post but Im going to ask again. The idle in this car im looking at hangs out at about 1500 rpm, and when you hold the rpm steady, lets just say 2500, it will drop to 2000 after about 5 seconds then rise back up kinda slowly, then in another 5 seconds it repeats, what do you think it would be. Its an 87 tII by the way

 

Could be a vacuum leak or the fast idle cam working in an improper fashion or a combination of both.

https://www.rx7club.com/showthread.p...dle+cam&page=3

 

im no expert, correct me if wrong
but the throttle jumping up and down (not steady) sounds like somthing to do with the thermowax or coolant flow to it.

 

If there is a weak flow of coolant to the thermowax then that would cause the roller cam to not roll off as quickly as it should or roll not enough which would either take the car longer to idle down to a proper idle or stay at a higher idle than it should be at. It should not cause a jump in the idle. The only way that could occur is if the thermowax was heated and cooled at an extremely rapid rate, which would cause the primary throttle plate(s) to open and close in rapid fashion, which is not realistically possible at all.