99 Disco engine cuts in and out on the highway

[rkatk]

This seems to be a problem common to many Discos but not much concensous on the fault. When driving on the highway my 99 Discovery I will slow down for a couple of seconds and then immediately speed back up again. This happens intermittantly, sometimes once and sometimes four or five times in a row. Never actually shuts down, no idiot lights come on.
I have read some suggestions that it may be the engine vehicle speed sensor, another sugestion was about some thermostatically controled device beside the transmission?
Who out there has had this same problem and how did you solve it?
Thanks,

 

[joey]

2 things, does the speedometer jump around? If you change to 3rd gear does the issue go away?

If yes to these questions it is the VSS.

If no then it can be a ground issue at the ECU.

 

[rkatk]

Joey,
No the spedo does not jump around. I have not tried it in a different gear.
Thanks

 

[Disco Mike]

D1 or D2? Try diving in either 3rd. gear or shift to Sport Mode if you have a D2.
How many miles on the truck?

 

[rkatk]

Mike,
158,000 miles. I got it to do it again today and shifted it into 3rd but no change, it still would slow down for a couple of seconds and then speed back up.

 

[bkas1977]

when does it happen? Is the electrical system loaded (light on, heater on, wipers, etc)
is it wet out when it happens? could very well be the vss or an electrical issue

 

[rkatk]

happens on the highway at 60 -70 mph. No electrical loads, dry conditions.

 

[joey]

I have the same issue on my 97 Disco (just haven't taken the time to troubleshoot it because I work to bleeping much lately.

I have been told by a very good Land Rover Mechanic 2 of them actually that this is normally caused by a ground or corrosion in a connector to the ECU if it is not the VSS. It can also be caused by a corrosion issue in the engine bay fuse box.

When mine has time to take a break in life, I plan to find the issue, but until then it hasn't died yet in the last 7.5 years of ownership.