Speedometer Q

[Mennis]

Hey guys, my speedometer's been acting weird and was hoping someone could help me out.  I couldn't really care less about the speedo but it seems that when it acts up, my car's (91 240sx) idle becomes unstable as well (drops really low when coming to a stop, bobs up and down at idle)

The problem with the speedo is that it often pins itself to the max even if i'm not going fast.  I was told that any problems with the speedometer (speed sensor) would not affect performance but that doesn't seem to be the case here.

Is there anything I can check that may affect the speedometer that could also affect the idle?  I looked at the numerous idle threads but those solutions didn't work.  

Thanks,

Dennis

[HKrpS13]

i had the same problem.
i had a mechanic and he told me that there's something wrong with the computer