1993 Lumina

Start by replacing the battery as a test if it's more than four or five years old.

There's no polite way to say it; GM went from the second best generator to the world's worst pile beginning with the '87 models. Due to their design, they develop huge voltage spikes that interfere with computer sensor signals, and they can destroy the diodes and internal voltage regulator. It is real common to go through four to six generators in the life of the vehicle.

What many professionals are finding out is to reduce the number of repeat failures, replace the perfectly good battery at the same time. As they age, they lose their ability to dampen and absorb those spikes. The battery will work fine in an '86 or older car. You might get lucky and not have any damage yet to the generator. That's why I'm recommending replacing just the battery first.

A year-old battery should be fine yet. Did you unplug the generator and try driving the car? If that doesn't help, which would surprise me, the best approach is to find a mechanic with a scanner that can display live data while on a test drive. Most of them also have a record feature. You press the "record" button when the stalling or surging occur, then play it back frame-by-frame later to look for glitches and dropouts in sensor signals. Since that data goes through the scanner's memory, the recording actually begins a few seconds before you press the record button.

Something else to keep in mind is the fuel trim data stored in the Engine Computer will be lost when the battery was disconnected. That data will rebuild as soon as you start driving the car again, but you will likely not even notice that is taking place. What's more important is the computer might have to relearn some things such as when to be in control of idle speed. Chrysler's relearn procedure is real easy. Volksawagens require the car to be towed to the dealership after simply reconnecting the battery. I don't know what GM's strategy is but it can't be too complicated because I never read about that issue with them. It would have to involve just driving the car. If the problem still persists, have the generator checked for output and "ripple". If ripple is real high, a defective diode is suspect but the symptoms should have cleared up when the generator plug was disconnected. That ripple, which is a rapid variation in voltage, interferes with sensor signals and confuses the various computers.