Exhaust valve???

Have a reputable import technitian diagnose your cars' problems. You've obviously thrown parts at the problem with no resolve. Yes, you can replace bad valves on the cylinder head if you are capable of that kind of work and/or you've done it before. To do the job properly/completely, you'll want to rebuild the entire head with all new valves & springs, have the head cleaned and throughly inspected by a reputable machine shop.