Why is the car stuttering and losing power going through the gears 1999 626-- auto?

Why is the car stuttering and losing power going through the gears 1999 626-- auto?
Naturally enough it could be a lot of things. Assuming the car's timing is okay (you've had it serviced recently right?), if the stutter is caused by a misfire then you need to look at the ignition system -- in your situation this will often happen if you accelerate really hard (i.e. put your foot to the gas) and the engine sounds/feels like it's about to stop.

Start with the spark plugs to make sure they're clean -- no build up of gunk around the point or any burn marks (shudder). If they're not looking good replace them and see if that helps.

If the plugs are okay it might be the ignition leads, which go from the top of the engine to the coil -- there's a lead for each cylinder and the coil is a little box thingy on the front right of a 4-cylinder '99 626. Unfortunately if it's the leads you're not going to know until you replace them. But it's cheaper than the coil....

Next is the coil. If you've made sure the plugs and ignition leads are okay and the problem persists, you might need to replace the coil.

All these things you can do yourself, but beyond that you'll need to see a mechanic.

Another possible issue that comes to mind is a seriously dirty transmission. Have you had that serviced in the past 3 years...? If not that could also be an issue.

Hope that's of some help, but as before, with cars the problem could be any number of things.