Trouble Code 24?

I read my computer codes the other day and a code 24 (speed sensor)came up. I have an 86 SE 2.8 L v-6. with 137,000 miles on it. Where is the speed sensor located, can it be tested and how? The speedometer is working. In a previous plea for help I described the stumble/jerking/misfiring that I get just as I start to depress the gas pedal(in all gears). This occurs at the point that the car is maintaining speed. Caosting and accelerating doesn't cause this situation. Do you think the code 24 is related to this condition?

Thanks,
Tom