Model TR 1001 here a while back when I switched it off the idel would stay high,but putting it in gear and putting some pressure on the clutch it would idel back. Now it won't idel down at all, so I took it off and open it up and on the inside theres a diaphram on the top where a 12 volt coil sets the other end has a slide rod that lets fuel by when it moves back and forth,now again I am guessing. I put it back on and now it rev's up and down like a govenor that dosen't have enough tension on the spring. theres four fuel lines that goes to it I believe three of them are on the return line and the other from the injector pump. This is on my 89 Autocar with a 300 cummins