I just bought a 1990 4runner and have a slight sag in the rear. I want to what kind of springs to buy and or shocks for a better and level ride.

 

There are a lot of different options that you can go with when replacing the rear springs on a 2nd Gen.
First welcome to YT. Then to find a bunch of info of almost any kind you may want to try the search option near the top of the page.
Now onto the springs. It really depends on how much weight you plan on carrying and if you plan on doing any other mods on the rear suspension. Downey Off Road Products and Performance Products have good replacement springs. If you are going to load your Runner down you may want to look into some FJ-80 rear coils as they are much taller and will not sag as much under a heavy load. The shock options will also change depending on the direction you go with on the rear springs.
Do a search with something like "2nd gen rear springs" and look at what some others have done and this may give you a little more info so you can make a better choice for your specific needs.
Good luck and be prepared to spend some money on some very good improvements. It is worth every penny !

 

I noticed the same thing when I bought my 4Runner, and replaced the rears with Eibach coils. They're great - the back is slightly higher than the front.

If I had it to do over, I would go with one of trdparts4u's OME kits and do the small lift at the same time...

 

https://www.yotatech.com/forums/showthread.php?t=54794

 

Thanks for the advice. Just got done putting on Performance Products H.K. made in Germany rear Coils. Brought it up real nice. The back is slightly higher than the front and noticed a big difference on the body roll in tight corners..great.