I have John Deere 3038E , having the same problem at 140 hr. the diagram does not match my tractor. where can tighten the throttle level. Thanks in advance.The friction device on your throttle lever needs tightening. In the attached diagram, items #7 are two nuts. Loosen the first one and then tighten the second one until you get lever tight enough to stay in position. Then tighten the first nut against the second one to hold adjustment tight.