Can an incorrect valve lash effect your idle?

Im trying to figure out why my idle drops from 900 to 600 and sometimes below that when I come to a complete stop.

I have Kenji's p28 and it seems to do it with his program more frequently than with my stock ecu. I've checked vac. hoses for any leaks, nothing. I've also been told that a lightweight flywheel could be why it drops? Any truth to that?

Anyhow, any suggestions would be great.

 

Ecu can greatly effect idle. If you just put it in and its doing it, the computer may correct itself over a short period of time and idle properly, however you could always open up the idle screw a little.

 

do a valve adjustment

 

Oh and to add, if lash is to tight, it will idle low. If its to loose it will be loud and may have idle problems.