Volvo engines?

[VolvoPaws]

My 850 T5 runs well, but if I maintain a constant speed on a flat road with the accelerator steady, the engine seems to falter very slightly before picking up. The speed dips and rises by about 1mph. It's so slight that passengers don't notice it, but it detracts from a smooth drive.
On idling, there is a click from the engine bay, every 10 secs or so, when the idling speed picks up or drops down. I don't know if this is what is happening when the car is moving, or if it's normal for a Volvo engine.
Any ideas?

[SaffronC70]

Hi there, does the car have air con ?

Chris

[VolvoPaws]

Hi. Yes, and the effect is as if the Air Con was turning on and off and taking power from the engine, but it happens with the Air Con turned off as well!
Gareth.