Check Engine Light, Passes Diagnostic Readings on 2005 Mazda RX-8

Vehicle will on occasion go over 35mph (on occasion) go over 5000 rpms. Standard AutoZone Reader will not pick up any codes for the check engine light, nor will the Genesis (Unsure of model). Pulled spark plugs, needed replaced, one of the four only had half a tip (Replaced all). Checked for air restrictions while doing this I pulled the Mass Air Flow sensor, after plugging it back in it ran fine for a quarter mile then same issue, replaced MAF sensor, still nothing.

Asked by for the 2005 Mazda RX-8
I wonder what caused one of the spark plugs to "wear off" was it detonation?
I would want to find a scan tool that will read the code if the check engine light has come on a code is definitely stored in the computer. We have three scan tools where I work it is funny how there is supposed to be a standard but occasionally one tool works better on one car than another. You will need to isolate what the code relates to before you can start diagnosing the problem.
Not sure what had caused the tip to "wear off" all four spark plugs were pretty corroded, and if I had been able to fix the engine light issue (whatever it is) myself, he probably would have come back in a cpl months to get help with the spark plugs.

After I had wrote this I took it to a garage and he put his genesis reader on it, passed once again, but going through the individual readings, found that the throttle was reading 21% at idle and to the floor was reading 68%. My friend dropped it off today (his car) and the tech is supposed to talk to another one of the shops in town to get another reader to try to pull the codes...I'm a mechanic in the Army with only limited tools at the house to be able to diagnose any "civilian" issues, its very frustrating, and I hate trying to "shade tree" automotive jobs *sigh*.