I have experianced the same problem recently (see post 'Surging idle' on May 1). My problem seems to have been solved by adjustment of the basic idle mixture at the AMM. It did not take much change of the mixture screw to smooth out the idle. I found a vacuum gauge helpful in setting the mixture. When the mixture was off the vacuum was low. Also, ever surge cycle caused the gauge needle to sweep. I also checked the mixture using a digital voltmeter to get the voltage to cycle from .3 to .6 volts. I have read other posts saying the reading should cycle from .1 to .9 volts, but I was unable to get this large a span.