I have 2001 Volvo V70 that's been acting up lately. The car started "stuttering" when accelerating up hill. As I'm pushing down the accelerator, the car will stop accelerating (RPMs remain constant), and the engine feels like it may be slipping.

We've also felt this happen when the car is in park and not moving. It also seems like the problem is worse when we are blasting the AC. Does anyone have any idea on what could be causing this?

I am scheduled to have the timing belt, tensioner, idler pulley, water pump and spark plugs replaced next week. Could this problem be related to any of these parts?

Thanks for any advice!