I realize you're talking about a Gen 1 GT, but my Gen 3 SDR threw the MTC code after shooting across some abandoned RR tracks passing a truck. The dealer reset the cables to the exhaust valve with the computer and cleared the codes. Then, as Trebor27 suggested, I installed the Healtech ESE (exhaust servo eliminator) and haven't thrown a code over the following 9000 miles. Best of luck.