Scan tool
All the tools mentioned so far are great and I use Turbo link, because I can sit down later and analyze the test drive. The tool I use when I have a problem and need to fix it fast is the Autoxray EZ-Scan 6000. It will work on any car not just Buicks. It will work on OBDII, GM OBDI, Chrysler, Ford, and most foreign cars. It will capture data to down load into my computer. It will give me direct readout for ignition retard, O2 readings, TPS, IAC, MAF, What gear the trans is in, Coolant temp, Engine load, RPM, Loop status, Ign timing advance, short term fuel trim, vehicle speed, just to give you an idea. It will capture trouble codes and explain what the numbers mean. They make several models, but the 6000 is the one to get. The only thing better is snapon and the cost is to high for me.
I think the link is Autoxray.com