idle problem

Hey lads, just back off two weeks hols and brought car out this morning and she is idling weird is hoppin from 1000 to 2000 and back down again but seems to be driving perfect, after bout 20 min driving the emmisions light came on. Any help welcome, oh ya its a 04 wrx.

Thanks.

Car

Sounds like it might be the maf sensor. This will cause the idle to hunt up and down and can cause the car to run rich which would give you high emissions.

was the battery flat???
did it need a jumpstart???

No battery was grand didnt need a jump. The idle problem seems to be gone now but the light is still on.