1992 Buick Lesabre recent low idle

As of 4-26-08 my buick has had a lower than normal idle and now I have to slightly press the gas pedal down to start it.
Within the last month, I have replaced the sparkplugs and wires, the trans fluid and filter, engine oil and filter, and fuel line. {Within the last 3 years, the radiator, the heater core, the fuel filter, the tires, alternator, new battery, and a new timing gear set}
It had been running normal until the low idle. With the low idle the engine does seem to run just a very small amount warmer.
(might this be related to the summer blend of fuel in California?) Any ideas would be appreciated, Thank-you.