I'm gonna try to explain this as good as I can. I don't know much about cars, so try to be patient with me. Here's the deal. I have a 1997 Honda Accord LX (4-cylinder engine, automatic transmission), 140,000 miles.

When I first bought the car, the guy who sold it to me informed me that it needed a VSS (Vehicle Speed Sensor). Which was true. The speedometer didn't work, nor did the Cruise Control. My girlfriend's father (who's a professional mechanic, and also went with me when I bought the car to check it out) put in the VSS for me and the Speedometer worked fine. But the "Check Engine" light was still on. After hooking the machine up to it, I found out that I needed an Input (Mainshaft) Speed Sensor. So my gf's father replaced that as well. After it was replaced, the Check Engine light went off.

Now here's the issue. When my gf's father replaced the VSS, he told me that one of the circuits on the part that plugs into the VSS was corroded. But now...my car shifts funny and the speedometer goes all over the place. For example, I might be doing 45 MPH, and the speedometer will just jump to 80-100 MPH and keep bouncing back and forth. And when this happens, the car begins to jerk while accelerating. The check engine light hasn't come back on since replacing the mainshaft speed sensor. While idle, the oil light flashes on and off (I had an oil change a couple of weeks ago). This has happened for 3 straight days. My gf's father is out of town, so I can't have him look at it. I suspect that it has something to do with the corroded circuit in the VSS, but I don't know about cars, so I could be wrong.

Since I've bought the car, I've had the oil changed, installed new wires and plugs, and also, the transmission fluid looks to be in great shape.

Any idea what this could be?

 

I would try to clean the corrosion off the pin.