Filled tank with gas and rrove about 50 miles. Went to a meeting and began driving back home. The engine misfired or hesitated, then ran OK.
About half way home the "CHECK ENGINE" LIGHT CAME ON STEADY. but the truck ran OK.
After about 4 days the light remained on so I had the dealer read the error code. It indicated that the Mass Air Flow sensor was out of range. They recalibrated the sensor and the light went out. They said that "sometimes" this will fix the problem.
It fixed it for one day and the light came back on. The mechanic also asked me what grade gas I was using. I told him mid range and he said it was OK to use 87 octane instead. So I switch to 87 or regular.
In the meantime I cleaned the MAS with an utrasonic cleaner (the type you clean jewery with) using purified water and then dried the sensor with air.
(suggested by an Engineer that manufactures MAS's for another company, Not Bosch)

Now the light is off part of the time and on part of the time. I will be switching back to mid grade gas ASAP.

Now I don't know if it's the MAS sensor or the regular gas.

Anyone have any input? Is gas Octane a real potential issue?
Thanks