Toyota Repair: 2004 Toyota Camry XLE Tuner, air fuel ratio, toyota camry

Question
QUESTION: I do most of the maintenance work on my 2004 Toyota Camry XLE. I am not a professional mechanic but I enjoy working on my car. I bought a pretty good OBDII scanner I would like to know where I can purchase a Tuner that will allow me to reset or modify the onboard computer. (For example raise or lower RPM.)

ANSWER: I don't know of any such tuner, maybe they are available from an aftermarket source. If there is an idle malfunction it's usually due to a malfunctioning component such as the idle air control system, the computer adjusts the idle speed and air/fuel ratio based on inputs it receives from various sensors.

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QUESTION: The main reason concerning a computer tuner to be able to control the RPM is because when my engine is idling with the AC off the engine runs very smooth, but as soon as I turn on the AC the RPM drops quite a bit and the engine vibrates. What could be causing this problem? By the way I have a 4 Cylinder Engine. As far as the Tuner is concern maybe is not called Tuner I don't know what is call in the auto industry but I would asume that dealers and repair shops are able to make RPM corrections if they have to.
One more question, I've been thinking of switching from conventional oil to synthetic is this a wise decision? (I live in HOT florida)
Thank You in advanced for your time and attention to this matter.

Answer
Dealer technicians can not make rpm corrections, there is nothing to adjust as the computer does this based on various input signals from sensors, if there is a problem with the idle it's due to a component or sensor failure, most idle problems are caused by faulty or sticking idle air control (IAC) valves. I can't advise or recommend non factory repair/adjustment procedures. As far as the oil is concerned you can switch to synthetic oil at any time. The advantage to it is that is has longer interval changes than regular oil.