c200_lahore

I have c200, w203 and lately it has developed hunting at idle upto 100 rpm and at times even more. This is irritating and I have also seen that fuel consumption has increased a bit. I have its vacuum pipes (set of three) with valve changed and now there is an electronic valve with one way valve and pipe suggested by my mechanic to replace but I have doubts it would help. At cold start, the engine hunts the worst. Any cheaper solution please?
Thankyou.