Another thing that might help for this is to connect a scanner with "record" capabilities, or a type of flight recorder that you control. When the problem occurs, you press the "record" button, then the mechanic can play it back slowly later to see what changed. Because that data passes through the scanner's memory, the recording actually starts a few seconds before you pressed the button.
That is fairly effective with intermittent running problems on older vehicles but for electrical problems it could also affect the power source the vehicle supplies to the scanner. Losing scanner power could erase anything it memorized or recorded. On newer vehicles from the last five to eight years, there are so much electronics and computer controls interconnected, that seemingly unrelated computers can cause the problem you described. Diagnosis of those things can be easier in some cases thanks to all the computers, but when no codes are being set, finding the cause can be real frustrating, as you're finding out.
Thursday, June 28th, 2012 AT 8:11 PM