I'm currently driving the volvo s60 2.0 LPT (light pressure turbo) about 3 years now.

A few weeks after the last servicing done sometime in August, I notice that whenever I start the engine followed by switching on the aircon, and then putting the gear to either R or D, the tachometer jerks violently between 700 and 800 rev/min and the car vibrates. (The usual steady tachometer reading at engine idling is about 750 rev/min.) At the same time, the headlights and interior lightings would flicker as the tachometer jerks. There was once when the tachometer jerked so badly that the eingine actually stalled.

However, this jerking does not happen when I put the gear to P with aircon on, or when I put the gear to R or D with the aircon OFF. It only happened when I put the gear to R or D with the aircon ON.

Is this the problem with the engine, aircon or gear transmission? Otherwise, the aircon and transmission are working perfectly.

Please help. Thanks.

 

One possibility could be a dirty or faulty throttle body. You could try cleaning it first.If not it could also be software related do you know if the car has all the lasted software in it?If you are still in warranty take it to the dealership and have them look at it.