I have 04 RX eight and I’ve been having an issue with the car going into a limp mode type deal the idle randomly begins accelerate and I lose functionality in the gas pedal and I have to shut down the vehicle and unplug the mass airflow sensor and plug it back in to start it back up I get the error codes P2109
And P0638

 

Sounds like your throttle body or gas pedal are having some problems. You have the codes, does that mean you have an OBD2 code reader? Perhaps you could troubleshoot a little by monitoring the throttle position sensors associated with the pedal and throttle body if you can with your code reader. If not, maybe you could visually inspect the pedal and the inside of the throttle body to see if anything looks damaged or dirty. If you don't learn anything from that maybe you can do some tests with a voltmeter too.

 

Try doing the Google search option with: Site: Rx8club code p2109 p0638 in the search bar. Many posts about the throttle body that may help.

 

I have a exact same car for parts sitting right next to mine and I took the throttlebody and the gas pedal off from that one and put it on mine thinking that that would solve the issue but it’s still having the same issue the only thing that I noticed is that I have an aftermarket air intake that doesn’t have a purge valve I did clean the parts before installing them but explain more about the voltage testing

 

I was thinking maybe you can apply a voltage to the potentiometers on the pedal and throttle body to test that they are outputting the expected voltage as you move the pedal or throttle body. But since you replaced them with other parts and you still get the same results that's probably waste of time. If you can find a service manual for an rx-8 maybe you could find the proper procedure for diagnosing this issue and the possible culprit part?