I have a computer expert on Tune port and Corvettes. He's actually scratching his head. This guy worked for GM for years. The carbon build up was caused by the return line from the fuel regulator was blocked. Car was running down the road with 78 lbs. fuel pressure. Running really rich and surging. Fixed that problem and now runs great just stalls on deceleration. PVC is clear and vacuum port is clear also. No codes at all on computer scan. Says everything is normal. Crazy