Just put $2500 in repair for the 2003 Diamanté includes ,belts ,plugs,wires

What is your question?

Fuel system cleaned out and new servo kit,the car wants to shut down with no codes while coming to a stop in traffic,runs excellent in garage and highway,No codes appear according to the dealership,I plan on taking it back but unsure if they know what is going on.I am not burning oil,this car has been babied since I purchased it in 2003,she has run only on Royal Purple and I use all K&N products plus high grade fuel,they adjusted the throttle cable Friday hoping to up the idle,she shut down five times in town Saturday,any ideas I think its a sensor or injector