In reply to MrJoshua:
Anything past 1996 will store long term fuel trim. An intake cam advanced a tooth will greatly affect fuel trim, and it takes a while to learn. (Short term is keeping the O2 on the bubble, long term lowly walks in based on the trends that short term has been taking in a given cell)
Disconnecting the battery may not do anything on newer cars to reset learned parameters, but on a 90s car it should work if one doesn't have access to a scan tool.
