Impreza Outback Sport Jerking/Jumping When Changing gears

I have a 2002 Impreza Outback Sport. Since moving to Tucson, AZ, from Flagstaff, AZ, the car jumps when changing gears (I have a manual) as if I was back in the day of learning how to drive a stick shift. This only happens in the summer, when temperatures get up to 110. Also, the idle is very rough and the car almost stalls when stopping quickly (this is infrequent). Any ideas what’s happening with my car?

I would suggest taking a look at the Mass Air Flow Sensor (MAF).
A gunked-up MAF could cause these symptoms.

Could be any of a number of things, but the idle problem makes me think it is this. When you take your foot off the gas (like to change gears) the ECM detects this, and think you are trying to let the engine idle, or pulling to a stop, so to save gas it completely turns off the injectors. Then the engine rpms drop, then when you put your foot back on the gas, it knows you don’t want to stop but to continue instead, so it give you at least enough gas for idling. This transition from no gas at all to idle can cause a jump sensation if the idle speed is too high or if the idle is rough. I think it is a good idea to check the idle speed and idle ignition timing as a start. I doubt youwill be able to solve this problem until you are able to return the car to a good idle. How’s the routine maintenance? On the schedule in the owner’s manual, or behind? If behind, you know what to do. It would be a good idea as part of all this to test the throttle position sensor btw.