Sounds like a dog barking! Help!

Hi. Got Octavia 1.9tdi 110bhp 52 reg.

When accelerating, usually on an incline the pull bounces and sounds kind of like a dog barking. It happens intermittently, normally at 2000 revs and usually poor engine performance follows which is rectified by restarting the engine.

My local garage found no fault codes but replaced a vacuum hose which has put an end to some hissing, but the car behaved itself on their test drive so they cannot identify the fault.

Its done 86k had new clutch and cambelt in the last year.

Prior to my ownership the car had sat on the previous owners drive for a year without much driving, if that helps. :(