Rough idle & bouncing speedo

[PHeller]

1989 S13

Whenever I go over a crest in the road, or steep quick elevation changes (like over a hill or around an off camber turn), the speedometer dies and will randomly come back on again. The speedo isn't off in its speed, but it just goes dead...as though there is a wire that shorting somewhere or something hitting making it lose connection. Any idea where to check this?
Modified by PHeller at 8:47 PM 12/28/2008

[PHeller]

bump?

I can't seem to find any thread similar to this topic.

[gingerbredman]

i wish i knew something about it

i've got a similar problem, my speedo stays on 0mph half the time, the other half it's flicking to 115 and back constantly. i'm guessing the speed sensor, but i haven't really looked into it yet.

does your car cut off before it pegs out?

[Eddiemac]

Ive replaced the speed sensor in two cars, one the speedometer didnt work at all and the other dropped to zero everytime I hit a bump. Try swapping one in that you know works. Sometimes you can tell they are bad just by looking, but more often than not, they look fine and are just wore out.

[gingerbredman]

hey one more thing. on the pass. side of the transmission there is a 2-prong sensor that was disconnected, i hooked it up and the speedo worked for about 1/4 mile then pegged out and hit 0 and all that mess. i checked afterwards and it was still connected.. do you know what the sensor is? it's beside the speed sensor i think

[PHeller]

Well I think I've got something else adding to this.

It seems that whenever my speedometer dies, the car cuts out for a split second, as though its hitting a limiter.

The exact cause of this ranges from the speedometer, speed sensor, possible shorts, etc.

Does this change anything?