When I accelerate from a stop my speedometer needle will stay at zero then all of a sudden catch up to my actual speed usually around 20-30. It will be fine when driving but does this every time I start from a stop with anything more than say 1/4 throttle. Anything less than 1/4 throttle and it behaves normal... Right before this started happening from a stop my speedo would jump from 0 to around 30mph then fall back to my real speed. I have no clue what could be causing this but I figured someone out there might be able to help me fix this problem.

Oh it's a 2000 3.8 auto 60,000 miles

 

it can be a fualty speed sensor or the wires going to the sensor can be grounding out each other and when you accelerat they are separating. My brother had a 97 and he had a similar problem and when we went under nieth it we found that there was a oil leak that ate away at teh ruber that insulates teh wires. if it is not one of those 2 things than you may have striped gears inside your speedometer.

 

First thing I thought was speed sensor but i looked at some online part stores and I can't find a speed sensor for a 2000 3.8 stang? Does my car have one and if so where is it located? Also I noticed the cruise control sometimes disengages by itself and other times works perfectly. I'm gonna check the fuses today and see if I have any blown ones. Other than that I'm lost.

* I just checked the fuses and they are fine. I also did the guage sweep test in the diagnostics mode and it looked good. But when driving with the electronic speedo in the diagnostics mode the digital readout also stays at 0 with the guage then jumps all of a sudden to the actual speed.

 

Well I figured out the cruise control works on flat roads but once you hit a hill and the tranny downshifts the cruise control disengages. Also I've noticed the one-two shift is sometimes strange when the speedometer finally moves and catches up with my speed around 20-30mph. Could it be a bad computer/sensor?

 

Alright I reset the ecu by unplugging the battery overnight and my gauge is still going haywire. In the video I have it in drive and my foot on the brake and giving it a little gas. It does the same thing while driving but worse, but I didn't want to drive and film at the same time...
http://www.youtube.com/watch?v=JR0zLCT-Gdg

 

It has one, may not be called a speed sensor thought. It plugs in to the trans where the speedo cable used to plug into on the older models. When you look under the car look towards the back of the trans where the driveshaft connects to the trans. around there you will see it.

 

Anyone know what this part is called? I can't find a replacement anywhere online.

 

This weekend my car "fixed" itself and was working flawlessly. But this morning it was acting up again. This time the speedo was jumping again and when going up a hill the tranny was shifting in and out of gear like crazy. So looks like i'll be making a trip to the garage. I sure hope i don't need a new transmission the car only has 60,000 miles.

 

check your engine ground strap

and its called a vehicle speed sensor, and it SHOULD be mounted on the drivers side of the tranny

 

If the transmission is giving you a hard time, like Adder said...it's likely your VSS.