reds61on
Member
This is a 1986 2.9 A4LD 4x4 Supercab truck that I bought for $500 with 66K original miles. It had a significant vibration in OD but was not present in drive at the same speed. I searched the Internet for possible causes including this forum. One of the possibilities was a miss that would be noticed in OD due to the low RPM. Wanting to go with least cost first, I changed the plugs to Motorcraft coppers. Found a crack in the porcelain on plug #5 (splitfires that my dad swore by but that I don't). Long story short is that my vibration in OD no longer exists and was due to a miss. Obviously the truck runs much better as well. I know that OD vibrations are not always from ignition spark issues but wanted to share my experience. 
