Toyota Repair: Toyota previa 1993, hydrocarbon emissions, combustion chambers

Question
I am the owner of 1993 Toyota Previa.This vehicle is usually used for short trips. Lately it starts rough like missing (new high voltage wires an spark plugs and distributor were replaced) and white smoke is visible at the exhaust but if the hidling speed is held in place by slightly accellerating  it clears itself up and the idling speed picks us normally.The level of coolant it appears to be more or less at the same level in the expansion tank, no light shows up. I am a self doing person and I have a shop manual which indicates to be the ISC system. If I take it to the dealer to have it repaired it is going to cost me. Could you give me any suggestions, should I have it disgnosed from the toyota dealer?

Answer
The idle speed control valve does not cause an engine misfire just a low idle and engine stalling, the white steam from the exhaust is a cause for concern as it may indicate a headgasket leak, even a small leak into one of the combustion chambers will cause a misfire, there is an easy test to determine if there is an internal combustion leak and I would suggest having the test done either at the dealer or someone else that knows what they are doing to check for excessive hydrocarbon emissions in the coolant.