Whenever Ive just been driving and pull up the revs always go up and down when the cars idle. If I put the A/C on it stops!? Any ideas?

Also when reversing or pulling away at low speed theres a knocking sound over the rear left wheel...?

Thanks for any help.

 

I had bad idle problems a wee while ago, as documented on here.
Same symptoms apart from I dont have AC.
So I bought a brand new MAF sensor from subaru for about £75.
I also bought a lambda sensor from halfords (L300) for £25.
Disco!!
I have now regained my rock solid idle for £100, bargain.
I also took ozzy`s advice and cleaned my idle solenoid.
quick ECU reset and Im a happy camper again.

Peanuts