i had this wiggle of the speedo a few months ago. now my odo works but my speedo doesnt. doesnt bother me much as ive gotten really good at judging speed based on RPM in 5th gear
[MENTION=8372]yellow[/MENTION]Scorpian your cluster needs to be rebuilt, there is no doubt. Do it now before it gets worse. It can actually start a fire in your car...you're also going to get good at emptying your wallet
If you have handheld oscilloscope or even a multimeter, you can do a quick check.
If VSS is fine, time to refurbish your gauge cluster.
O-scope! That is some serious stuff!
I will admit to having 2 or 3, but I use them so infrequently it takes me longer to remember how to get it working than using!
Problems of having cool tools!
VSS is the vehicle speed sensor, called VSS1 in manuals. Look on page 23-133 in the 1991 service manual. It sits on top of the transmission casing above where the drive axles are. You can see it from above with a flashlight but need to remove the airbox or other components to gain enough room to remove the 2 bolts holding it on.
You can use https://www.amazon.com/gp/product/B01FAAL7R4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 (or part # 78410-SV4-003) as a cheap replacement, both versions with and without a wiring pigtail included will fit to the stock wiring harness but might be tight depending on your model year. The little peg in the pics ("joint shaft" in the manual) needs to be inserted between the sensor head and the transmission for it to work, the new sensor comes with a new "joint shaft" but you can reuse the old one too.
If you're curious you can take the top 3 screws off the old sensor head and look inside, I'm betting the electrical potting is messed up and smells like burnt plastic.