99 Saturn SL2, 140,000 miles…it lunges forward slightly when I’m braked at a light and is sometimes slow to accelerate when I want to start going again. Any ideas? I thought maybe fuel injector or tune up. Please help! Thanks!! 
There are a number of possible causes, but if the car has not had regular maintenance, it is not practical to “cherry pick” one symptom and try to resolve it until the maintenance has been taken care of. Otherwise, you will wind up “throwing parts”–one or two at a time–at the situation, and this is not the way to resolve driveability problems.
If the car did not have its last major service performed at 120,000 miles (probably the same procedures listed in the Saturn maintenance schedule for 60,000 miles), then that long list of maintenance procedures is what needs to be taken care of first. That may take care of the problem, but if it doesn’t, that will allow for easier diagnosis of the actual cause of the problem.