I just purchased a 1989 300SE with 155K miles. The vehicle had been sitting idle for several months before I bought it. I had a leaky valve cover gasket that I just repaired. The vehicle will not pass the Masschusetts emissons test. I was told by the technician who conducted the test it was running rich. I have put in some techron fuel additive and replaced the plugs. Several of the plugs I removed were wet but nothing outrageous. Do I need to make a mixture adjustment or continue to run to get rid of some carbon build up?