Oldsmobile/Buick Repair: Possible Speed Sensor Issue, vehicle speed sensor, buick park avenue

Question
Hi Van,
I asked this question of another expert, Ed, but he went on vacation before I could follow up. Would you mind following this saga and letting me know what you think?
What I wrote to Ed:

I believe you may have answered this question before, but not for my specific model/year car. I have an '89 Buick Park Avenue and driving to town this morning, the check engine light came on and at that moment, the speedometer dropped to zero and the odometer stopped as well. The car was going along normally and then it felt like I drove over the tiniest of bumps and the speedometer and odometer were back and the check engine light went off. This continued back and forth with the check engine light coming on and speedometer going off and each time it felt like the car was going over a little bump...not a lurch or jerk, no noise whatsoever. Fearing I would get a speeding ticket, once the speedometer was on, I turned on the cruise control, drove the last few miles to get home and the issue didn't happen again.

My husband is truck driver and is pretty handy mechanically...I was hoping to be able to give him the good and bad news and be somewhat prepared with parts? and information for repair.

Ed's answer:
You may have a faulty connection at the Vehicle Speed Sensor,this sensor is located at the right side and on top of the transmission output shaft housing,it has a 2 wire connector,you will need to gain access under the car to inspect the connector and the wires,make sure the connection is good and also the terminals located in the connector,also look for any rubbing through of the wires and harness.let me know if you need more help.

In the time between asking the question and getting that answer, my husband has checked the speed sensor, the wires, the connections, etc. All appears ok, but the car seems to have developed a new issue - when the speedometer goes out and the check engine light comes on, the car idles very poorly, sometimes just completely dying. Sometimes I start the car up and it will be idling way too fast for a good five minutes before it gets to a more normal RPM. While putzing with the car, my husband discovered when he disconnected the fan, the car would start with the check engine light on, but it would soon go off and run normally for at least a while before starting up again. Otherwise, if the check engine light is on, the car runs rough, has little get up and go and I have no speedometer.

We took it to an Autozone to see if they could use their little hand-held diagnostic tool, but the technician got nothing but error messages, she tried the "old fashioned way" with some sort of key in the terminal-thingie where the computer had been connected and couldn't get that method to work either - apparently it is supposed to cause the check engine light to flash a certain number of times according to the issue, but we got nowhere.

Any ideas on what direction we should go now or what area we should be looking at? Could a short somewhere be causing all of these problems?

Thanks so much for your patience and time,

Barbara


Answer
Hello Barbara,
I don't know Ed, but what he said is very likely.
The ECM needs a signal from the vehicle speed sensor, and the speedometer and odometer also need it.
Ironically, the cruise control needs it also.

It is possible that a new vehicle speed sensor is needed. They are quite cheap at Autozone, and easy to replace.

A short i doubt, but an intermittent "Open" is more likely. Causes are loose connections usually.

A bad ground under the dash is a possibility, and if the cruise worked when you would have expected the problem to happen, it is possible that the cruise system was supplying a ground that is otherwise intermittently missing.

Those are very hard problems to nail down.

Van