348 speedo help

My 94 spider, the other day I was coming home and the speedo bounced around 140- 160, then came down to 55mph, while I am sitting at a light, also at the same time the miles are still going around like it is in motion calculating. The it went back to normal the rest of the day. Well last night I started it up and boy there it goes again while warming it up, go crazy and making it have more miles, so I disconnected the speedo sensor back on the trans, then restarted it, and it is still doing it, I am stumped any info

 

I pulled it apart and left it apart, wouldn't it stop working all together, and it is still apart, also if I clean the plug, what should I use to clean?

 

Also to more info, as soon as I turn the key like in accs, to start it is already bouncing, and my miles are going around and the trip miles going also, I have cleaned it now and plugged it back together , and checked all my connections are secure, any more info

 

Even with it unplugged it would still do it ?

 

Do u mean the sensor in transmission, I unplugged it , and still bouncing and adding