My 2001 SL1 4-cyl 1.9 has begun to do what I believe is called "stumble".
 

My Saturn has approximately 138,000 miles on it. I of course bought it used, about 2 yrs ago. Around the middle of this last summer I put a bottle of injector cleaner into the fuel tank, as prompted by an Autozone employee. I again introduced a second bottle a couple months later. It seems that in the last six weeks or so, since it has been 'wintery' for lack of a better term, my car has begun to "jump" or hesitate (my boyfriend describes it as almost stalling), however I don't feel it to that point.
It is generally when I first start out in the early morning or after dark nighttime when it is still a cold motor. It again, generally happens in second gear, although it has occurred in third and even first gear last night. For the most part though it is in second and I am accelerating into almost third gear.
I have been advised it could be nothing major other than an injector, or fuel filter or as bad as a pump (In the tank ? who's great idea was that one?)

I would like to take the time to let whomever is hopefully willing to advise me in this matter, that I am VERY mechanically inclined. My first (and only) husband, and a couple of other friends, answered all the questions I asked when they had been working on or building an engine, this was in the days when we had cars that were 'weekend' maintenance rides. I loved my 69 Firebird 400 bored out 40 over with a 400 tranny. She was a ticket getter! And then there was my 46 Ford pickup, I sat in the shed everyday until the 350 chevy engine was ready to drop in ( we had to take the wheel wells out to make it fit) she was a smooth one after that, but two boys and single I had to let her go cheap.
I guess what I'm getting at is that I know my way around a car however these new ones with fuel injection electronic ignition and a brain??? I need to learn more about. I don't want to have to sideline this one cuz something minor turns into something major of which a dog groomer won't be able to afford. Please Help. Peace & love, *ellief~.:

If it hesitates or misfires while accelerating, the problem usually is ignition related(plugs,wires, coil). If it misses at idle, it could be the intake gasket. That is a common problem on the SOHC engine. Would you describe it as a misfire or a hesitation off idle?
Injector problems on these cars are extremely rare.