On my 98 Wrangler 4.0L I was driving this weekend on the highway and the speedometer when you accelerate jumps forward and buries past the 100 mph mark, then dips back down and bobs around the current speed. Now it is also doing it driving around town when I accelerate. Are their any ideas on what could cause this? Your help would be appreciated.
Sticky speedo cable. My father says to put graphite into the sheath - I greased mine and it doesn't bob anymore - but I also live in an area that's predominantley 50deg plus. you should also look to see if the cable may be damaged. Such as been drug over a rock.
Another possibility; on some newer cars they use an electro mechanical sensor/transmitter deally in the trans/xfer case instead of a purely mechanical connection. This could also be kerput.