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.
Thursday, July 14th, 2011 AT 9:18 PM