Would vacuum have anything to do with this
 

I took my 190e to the shop to have the vacuum checked. They only tested the engine vacuum, but as soon as the wife drives it out of the drive way the speedo starts freaking out bounces up and down and few times and dies.

Does the vacuum have anything at all to do with the speedo operation on this thing????

No. Why did you suspect a vacuum leak?

I had already found one small hose near the fuse box that was cracked and just wanted to make sure there weren't any more leaks to contend with. Turns out there aren't. What would cause the speedo to do what it did?

The speedo cable or the speedometer is bad...
 

Do a search!

Did the shop remove the instrument cluster to repair the vacuum line?. If the speedo cable is not disconnected from the trans first before pulling the cluster there is a strong possibility that the cable will get stretched causing the speedo needle to bounce.

I had a 300zx one time and grease got up into the speedo cable and it acted funny like this. Wonder, is there any grease that could migrate up the cable?

No, shop only checked the vacuum on the engine.

Search produced no clues.

I've had several cars do that. Usually lubing the speedo cable does the trick, at least or a while. I tried the lube up idea on one car. I pulled the cable off the tranz and wrapped the tube of an aerosol lube to it with tape. After several tries and lube all over my face it worked. Then it bounced a few weeks later and I lubed it again, then I pulled the cable and lubed it from the top. But I think too much damage had been done by then and it was in permanant bounce mode.
My last car was a '91 Acura and it would not just bounce, but drop to zero, hover around 20-60mph higher than I was going, or even hover around 20-40 at a complete stop. Weird, must've been computer controlled. It rarely did it, not enough to bother fixing.