Definitely follow logical troubleshooting procedure, which means check the
simple stuff first.  That's always the mechanical things you can see and
feel.  Electrons are only detected by magic.

I've had this happen and it was something that dropped on the throttle lever
and jammed it.  Broken cruise control cable I think. The good thing is the
ECU will cut off the injectors before the engine self-destructs!

At least that's what happened in my case, but at the time I thought I
destroyed it.

Stuart