Re: Check Engine light comes on and off.
I may be wrong but it is my understanding that if the CEL has come on at some point then a code has been set and is readable with the ultragauge or an OB11 reader. If the light goes out it means that the system has been checked 'x' number of times since the fault was detected and no fault has been found, when it comes on again either the fault has re-occurred or a new fault has been found. As the light goes on and off I suspect it is the same fault that is occurring and fixing itself somehow. Read the code and that will be a good start to the final solution to the problem.
How a brownish tinge to the insulation on a wire can be diagnosed as the fault is beyond me, this guy must throw chicken bones against a wall to interpret auto problems. Stay clear of this moron, he has cost you enough. I hope you have the old RCM he replaced as there was most likely nothing wrong with it and you may need it one day as a spare, he will probably sell it if he still has it.