hi guys

I have a little problem here

I use auto 1.3 MyVi

I've changed my stock spark plugs to iridium and stock air filter to K&N on January
I feel the difference when pressing the throttle. It gives some 'kick'

the problem now is, I've just service my car last saturday (16/5/09) at perodua SS13 sc, and the 'kick' is already gone
that service was the 4th (14k km) and the items changed were
1) oil filter
2) engine oil (semi synthetic)
3) gasket drain plug
4) gear oil
5) radiator coolant

supposed that i change spark plug and air filter in that service but since i have changed them before, i told them not to change these 2 item

maybe the problem is the gear oil?

i also notice that the radiator coolant level doesn't change since my last check (a week or 2 before service). SC tipu kah?

thanks in advance