Hey guys, I'm hoping for some help on resolving an issue with a disco I've been asked to help fix.

I come from the BMW world, so I know hardly anything about these vehicles, however, I am mechanically inclined.

The issue with the disco is this:

At ~55mph, the vehicle will hesitate. It will sputter a bit, drop to 50mph or so, and then "catch", and pick up speed again. This will cycle, almost like a "surge", a constant speed-up slow-down that happens roughly every 5 seconds.

This is not a constant issue. It seems intermittent. It's not something that happens every time I approach that speed. It seems to come and go as it pleases. It also only seems to happen in 5th gear (the vehicle is a 5-speed).

The same issue seems to happen sometimes around 70-75mph, although it is less common and less noticeable.

My first thought was perhaps a clogged fuel filter, however, it seems to "rhythmic" to be something of that nature.

I'm hoping my description is adequate for some diagnosing.

Any help is appreciated

-Mike

 

First two thoughts off the top of my head are a fuel issue(pump) or vehicle speed sensor

 

My truck acts like this only not as bad if I get bad gas.
I am leaning towards a bad VSS.

 

I unplugged the VSS and haven't had the issue yet. The downside is the owner tells me the issue is very intermittent.

 

I had the same exact issue. It eventually worsened to do it around 35 as well. I unplugged the VSS and the problem never returned. I replaced the VSS and the issue returns when I plug it back in. It's most likely a bad wire somewhere in mine because it runs great when it's unplugged.

If it keeps running ok with the VSS unplugged, check the wires first.