I have a toyota celica 1994 model , running is OK am satisfied with speed but whenever am in idling the rpm goes up and down range from 300-900 rpm , I replace sparkplug, high tensionwire, pressure regulator still the same adz... thanks

Check out these areas:

. Idle Air Control Unit:

Zip Code Entry at PartsAmerica.com

. Ignition Control Module:

Zip Code Entry at PartsAmerica.com

AutoZone may be able to test the ICM for free.