My 1981 280ZX has been running rough intermittently. No rhyme or reason. Sometimes it does it when cold, and some times it does it when warm. Periodically it tries to overheat. I now have a fuel smell in the coolant surge tank. Ideas?? Head gasket perhaps? Or intake/exhaust gasket? I did a combustion test and it tested to be good. Coolant pressure test also was good. Compression test is good as well. Ran a boroscope down the spark plug holes and all looked well. I am lost.