Everything is fine when it's driving on the highway. Problem comes when parking backwards or stopping at the traffic light with the shifting gear at D.

The problem is that, with the AC on, the engine has a strong shake every 3 seconds. The idle for the RPM of the engine drops seriously or stalls. At parking or stopping, it drops from about 700 RPM to 400RPM or even lower. The AC is still cooling though.

The car recently got the Timing belt changed and the Tune-up.

Thank you very much for your help.

hope your car is on petrol, check air filter, spark plugs and fuel filter. some times ther may be a problem with your air flow sensor. if it is fuel injection, check injectors too

regards chinthaka from sir lanka