Toyota Repair: supra idle, blown head gasket, radiator hose

Question
I aquired a 1990 Supra non-turbo having a blown head gasket.  The car ran idled fine despite the gasket.  After putting on the new gasket the car will start easily but rev up to about 1800 rpm's and drop for a second to like normal than rev back up to 1800 rpm's and cycles even after the car is at full operating temperature.  You can rev the car up to anything over 2000 and the car runs steady and smooth.  I removed the intake again to check if I had damaged any of the gaskets, but no damage was found.  The timing belt was changed and I checked the marks twice, but I do not think that would have anything to do with the lack of idle.
Please help so I can get this car on the road.
Thanks,
Jaime

Answer
Most of the time this is caused by an airpocket in the cooling system, there is air in the cooling system that has to come out, this may take a while, removing the top radiator hose and slowly pouring coolant in it will help.
I hope that the thermostat was replaced.
The reason this happens is that the water temp sensor for the computer is exposed to hot air instead of water and then some coolant will come in contact with it and this constant variation will cause the cycling effect, you need to get all the air out of the cooling system and it will idle normally.