Hi guys, I have searched the threads but cannot find and answer to my question and I have looked under the hood to see if there is an obvious problem and I have a copy of the RAVE. I own a 03 disco with 92k on the clock, it has been regulaly serviced and i have no other issues that relates to this problem:
When I engaged the cruise contol the disco surges then drops to the requested speed but will not hold this speed constantly as it surges and drops off then surges again. When I am towing my large heavy trailer its fine but running with out it it does not hold constant spped even on the flat interstate.
Is this normal?

Thanks

 

I have a similar issue where it seems jerkey. It keeps a constant speed but it acts jerky while trying to maintain the speed. It does not do this when not in cruise.

 

Not normal - would look at replacing vacuum lines, perhaps a tiny split or pin hole. Just a few feet of tubing.

 

I found a recall for surging cruise control... It is a cruise control ECU programming issue that was supposed to be handled at a dealership when the vehicle was new.. I believe the recall starts with vehicles made after FEB 2002...
No: SB142
Ref:
Issue: 1
Date: 11/07/03
SERVICE ACTION
Cruise Control ECU Software Configuration Improvements
AFFECTED VEHICLE RANGE:
Discovery Series II (LT) 3A767790 to 4A832224
Build Date 26 February 2002 to 28 August 2003
SITUATION:
CRUISE CONTROL "SURGE" AT TARGET SPEED
Discovery Series II vehicles have a cruise control software configuration issue, that may result in a surge of approximately to 2-3 mph around the target speed.
RESOLUTION:
INSTALLATION OF UPDATED SOFTWARE
NOTE: This Service Action is for un-sold vehicles held in Retailer inventory only.
Prior to customer delivery of vehicles within the above VIN range, download the cruise tune using TestBook/T4 CD "Archive 21" or later. Both 2003 and 2004 model year vehicles in Retailer inventory are affected.
PARTS INFORMATION:
LRN0002LABEL Campaign Label Qty 1 (NOTE : Sold in quantity pack of 100)
TOOL INFORMATION:
TestBook/T4 disc "Archive 21" or later
AS400 WARRANTY CLAIMS:
H142 (Option A) Time 0.30 hrs.
Download cruise control tune

H142 (Option B) Time 0.40 hrs.
Download cruise control tune. Includes Drive-in/Drive-out allowance
DDW WARRANTY CLAIMS:
Warranty claims should be submitted quoting program code B142 together with the option code. This will result in payment of stated time and where applicable parts/miscellaneous expense.


The SRO information listed in the Table has been included for information only. Do not enter the SRO onto the claim.
Normal warranty policy and procedures apply.
Material allowance is included in labor operation.
REPAIR PROCEDURE
INSTALL UPDATED CRUISE CONTROL SOFTWARE
NOTE: It is important to verify that the unsold vehicle is subject to this Service Action and has not had the repair performed at the Port of Entry.
1. Verify that the vehicle is subject to the Service Action.
2. Connect TestBook/T4 to the vehicle and load disc Archive 21 or a later version.
CAUTION: The hand brake must be set and the transmission placed in the neutral ("N") position before undertaking the following steps.
3. Engage the hand brake and place the transmission is in the neutral ("N") position.
4. Turn ignition to position "II".
5. Depress instrument cluster cruise master switch to place it in the ON (switch illuminated) condition.
6. Follow the on-screen instructions and select "Diagnostic System".
7. Follow the on-screen instructions and select "Discovery, 2003MY".
8. Follow the on-screen instructions, enter the vehicle VIN and press "Continue".
9. Confirm the vehicle information and press "Continue".
10. Follow the on-screen instructions and select "Cruise Control/Petrol/Vehicle Maintenance/Tune Information".
NOTE: At this point, TestBook/T4 will read the tune values from the vehicle and provide a display of those values.


11. Compare the tune values to the values listed below:
12. If the vehicle contains different tune values than those listed in the Table perform the tune installation.
INSTALL UPDATED TUNE
NOTE: Download of the tune values from TestBook/T4 to the vehicle will take only a few seconds.
1. Follow the on-screen instructions in TestBook/T4 and select Program ECU/Set new tune 4.6L engine on the screen.
2. When programming is completed follow the on-screen instructions and select "Tune Information".
3. Note the tune values and verify that they match those listed in the table above.
4. Disconnect TestBook/T4 from the vehicle.
NOTE: The cruise control ECU requires some adaption time after programming. Whenever possible the vehicle should be driven approximately twenty miles with cruise engaged. Customers should be advised of the adaption process on vehicles where a complete length test drive is not possible.
5. Perform a road test and verify that the downloaded tune has resolved the issue of cruise surge.
INSTALL CAMPAIGN LABEL


NOTE: Campaign labels may have multiple Campaign numbers written on them if multiple campaigns are performed at the same time.
1. When all specified repairs have been accomplished, prepare the campaign label (LRN0002LABEL) as follows:
a) Place the label on a hard surface.
b) Use a ballpoint pen to neatly write/scribe in the bare aluminum areas of the label the following information:
^ Service Campaign code "B142"
^ Your retailer code
^ The date of repair
2. Clean all grease and dirt from the radiator support member.
3. Peel the completed campaign label from the backing paper and position it on the cleaned area.
4. Roll the label with the special roller tool to ensure proper adhesion.
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You can check for holes or slits in rubber hoses which is common like stated this usually results in not holding speed not what your explaining.

Or i have also seen this from the statement above which is more pertaining to your symptoms. A new cruise computer should fix this.

 

My 04 does the same thing it's annoying that's why I don't use cruise. I wonder if I take my car into lr here in Canada if they would still do that recall ill call and ask them

 

It wasn't a recall, it was a service bulletin, big difference. Recalls don't expire and are always paid for by the manufacturer. Service bulletins are only covered while the vehicle is in it's warranty period. (at least in the US, don't have any experience with other countries but suspect it is the same)

 

I just went out to find if I had a break in a vacuum line due to surging while on cruise control. I could not find anything broken, but I noticed the cruise bracket on the fender was moving a bit too much, about 1/2 inch. I looked under the fender, and the three nuts that hold it to the fender were loose. One was almost falling off. I tightened them all up, and now the surge is almost unnoticeable. It's still there, but I can manage with what's left. Before, it was stupid...