Q: Keep stalling when I slow down or shift gears

Engine stalling is typically caused by fuel or ignition system problems and/or faults in the air induction system (including vacuum leaks) and engine management sensors. If you request an engine stalling diagnostic, the responding mechanic will go through a decision tree that contains all the possible causes, until the fault is found. Typically, an initial step is to see if the vehicle’s PCM (computer) has stored any diagnostic trouble codes as such codes can provide critical clues as to the vehicle system or sub-system that is malfunctioning. A not unusual cause of stalling is problems with fuel supply caused by a plugged fuel filter or a poorly functioning fuel pump. There could be problems with the fuel injectors, too. Vacuum leaks can throw off the air/fuel ratio enough that the car will stumble. A stuck open EGR valve can cause stalling, particularly if other "weaknesses" exist in the engine such as old spark plugs or leaky (to ground) spark plug wires, defective distributor cap and so forth. Your best bet is to simply request an engine stalling diagnostic, and the responding mechanic will get this resolved for you promptly.