'91 3.1L V6 auto -- speedometer fluctuation issue

[gregory_gdp]

I did a quick search and didn't really see anything quit like my little growing issue I'm having with my Lumina. Last week I noticed that occasionally the speedometer would bounce around (only going lower than the current speed) the dial about 5mph.

It has progressively gotten more frequent and with a larger range of bounce until this morning when I was driving home and let off the gas (didn't hit brakes) to slow down for a traffic light and the speedometer bounced around from the speed I was going, 50, all the way to 0 and did this for some time until I actually came to a stop using the brakes. Once I was going again the speedometer increased normally and didn't fluctuate again. So the only real problem I guess is that the speedometer isn't keeping the correct speed after accelerating but it only happens occasionally. All the time the car itself hasn't had any issues moving or slowing down it's just the speedometer acting odd so far.

I stopped to look things over a little bit after that traffic light, I only noticed that the serpentine belt probably needs replaced (it easily depresses a good two inches and the tensioner pulley moves about the same amount which would probably account for the odd clacking noise coming from the Alternator area) and that the automatic transmission fluid was low (refilled). Once I continued on my way home the issue went away for now.

The belt will be replaced this weekend when I get paid but I'm not entirely sure about that pulley and if it's supposed to move like that when I push down on the belt.

Any suggestions for other things to look into or even a good explanation and solution to the issue would be greatly appreciated.

[jeffcoslacker]

Check the wiring to the VSS, relplace the VSS if it continues for starters.

If that's the problem, eventually shifts will get erratic and weird other things may happen.

If you have cruise control, see if it works when this is happening.

[jeffcoslacker]

The tensioner arm is spring loaded, it will move when you push on the belt, but shouldn't be real easy to move.

When they go bad they will hop a lot while the engine is running, and make snapping/clicking sounds...

There is an index and pointer on the tensioner body that indicates the amount of belt stretch. If it's way out of the index range, the belt is shot. If it's still inside, but making noise, you may need to check the pulley bearing or spring tension.

[gregory_gdp]

Thanks for the help. Sorry I haven't checked back for a while. I'll have to check those out.