idle / running prob

[adiboy]

hi, ever since i bought her 4 months ago its got and idle problem, if i start it up in morning cold it will rev at around 1400 then when it warms up it comes down and idles properly at around 800 and idles smooth. when shes warm and you then give it a spirited run it then idles at any where up to 1500 and sometimes the idle just goes up and down constantly. im a mechanic but not sure if these have an idle control valve or not, carnt here any air leaks but not 100% on that, if you try pull away slowly when its doing it,its like a kangaroo and wants to go then it pulls up then go again,(bloody embarassing)
the engine light comes on and the code reader just says that its detected an unusual high idle, you can put it out but will come on after its done it a few times.
any help would be much appreciated

also if anyone lives local to me (norwich norfolk) would be nice to go out in another one or they can drive mine as not sure if it drives as it should.
car has done 40k and full subaru history every 4.5k.
thanks
adi

[John Mc]

Dynamix is near to you... not something like the lambda sensor is it causing over/under fuelling? Is there loads of black soot when you floor it?

[adiboy]

ok, not noticed major black smoke under hard trottle but when i start from cold the smell from the exhaust is very bad must be neat petrol coming out or as you say overfuelling but i dont notice it when its hot.