well my 1991 GLEIS fastrike sneeze is back and more predominate when trimmed all the way down and also a stumble or skip at idle about 200rpms by tach, it will idle at about 900 then stumble down to 7 then back up and does this all the time the sneeze is mostly when trimmed all the way down not as noticeable when trimmed up,timing is right on check it last week plugs look good as far as color. What to check now?