I just adjusted the valves on 89 L98 after hearing ticking on start up. Did it running and did 1/2 turn after clattering stopped. On here is said 1/4 turn, the manual said full turn, so I tried half. Now it idles at 1200 rpm in park and 1000 in drive, and there is a big miss at 3000 and in the 4000 rpm range. Any ideas appreciated...

 

just drove the car some more and now is fine through the rpm range, the idle still is high, is it common to have to reset idle after valve lash adjustment?

 

It is not common to have to adjust the idle RPM after valve adjustment. If the valves were misadjusted to the point where they were not allowed to close, you may have such a problem.

Presuming that the "L98" in question is still an L98, complete with TPI, there is no real idle adjustment. Curb idle RPM is controlled by the ECM via the IAC. All you can do is set the "zero" point by correctly adjusting the minimum air position of the throttle plates, than allow the ECM to do its job.

Incidentally, if you are measuring RPM with the dash-mounted tachometer, remember that factory tachs are notoriously innaccurate. You'll need an accurate handheld tachometer to set the minimum air position and monitor idle RPM.