I have an 86 GT.
I am posting this solution because I cannot post to the archived technical section. I have noticed some people have had the same problem as I have had with no luck in resolving.
The following describes the elusive prblem I dealt with for some time and have now, with the aid of some really thorough mechanics have been able to fix.
The Problem - When cruising between 60 and 65 mph (approx 3000-3500rpm) with no load on the engine (cruising with steady rpm on a flat surface) the engine would begin to jolt violently (for lack of a better term - stammer, slam, sputter, hesitate, jerk) bam bam bam with a rythem until I backed off to under 60 mph or sped up to above 65 mph. It would not do it while decreasing speed or increasing speed.
The Solution - Two things
1- (minor but contributed to the problem) Bosch platinum 4 way plugs.
2- (the cause) A cheap distributor. There was too much slop in the shaft and the engine could not time properly, therefore the computer was receiving faulty information. The cheap distrubutor to be avoided is of the type that has a metal ring with triangles under the rotor rather the the better type which has the metal "fingers" that stick up into the air.
Good luck and I hope this helps anyone who needs it.
