I had the same problem a while back, and I basically ignored it because it would come and go with no explaination or and no repair seemed to fix it. Finally the light went on for a while and instead of 0300, the code was 1345.
The distributor gears in late 90's GM engines have a tendency to wear, which throws the timing off a bit. My suspicion is that the original 0300 code was the timing starting to get loose, since that code no longer occured and was replaced with the new one. Anyway, I replaced the gear and the 1345 code went away instantly.
Pull out the distributor and check the gear, if there is any wear, get a new one. You may have to order it or go to a dealer. The big chains usually only carry the entire distributor. It's not a hard job, just make sure (with a long screwdriver) that the oil pump is at the right angle for a proper seat when you put everything back in. That advice was missing from the Haynes manual and caused me a lot of frustration
Thursday, February 21st, 2008 AT 2:18 PM