I have a 1990 4runner 5 spd 3vze that I have recently tackled the Head Gasket on. I finished that job just to find out I had to strip down my whole motor again to replace the knock sensor whenever you remove the heads.

Finally I got the new knock sensor and wiring harness back in the motor but I go to run it and it idles fine. I drive for about 30 secs I get the code 52 knock sensor faulty then I slow down to an idle and it revs up and down from 600-900rpm every seconds or so up and down up and down...
It also seems to run rich...


Any idea's im going CRAZY!

 

With your initial description I'd have guessed TPS, but if you're getting knock codes, I'd guess you didn't replace the knock pigtail and it's bad. Rule of thumb is any time you have the manifold off, replace the pigtail.