Erratic cruise control

[mikeB]

I am one of the many people who have successfully fitted cruise control. My car is a 2005 2.0 HDi Multispace Desire (M59). The brake and clutch switches were already fitted so it was just a matter of fitting the stalk and programming the BSI.
The problem is that, once CC is selected at, say, 60mph, the speed then drops to about 55 before picking up and going to 60. It then allows speed to drop to 55 again then back to 60. The cycle period is about 45 seconds. My other car, a Picasso, maintains exactly the speed set. Does anyone have any ideas?

[MudFT]

I am one of the many people who have successfully fitted cruise control.

Apparently not!

[addo]

I'd say either your motorised TB is out of range (ie; worn tracks) or there are issues with one of the sensors (this includes the feeds to/from them). Have you put it on a Lexia or Diag to see what it says?

[mikep1973]

I am one of the many people who have successfully fitted cruise control. My car is a 2005 2.0 HDi Multispace Desire (M59). The brake and clutch switches were already fitted so it was just a matter of fitting the stalk and programming the BSI.
The problem is that, once CC is selected at, say, 60mph, the speed then drops to about 55 before picking up and going to 60. It then allows speed to drop to 55 again then back to 60. The cycle period is about 45 seconds. My other car, a Picasso, maintains exactly the speed set. Does anyone have any ideas?

Mine does exactly the same thing. The speed tails off slowly down to about 50mph, then it "wakes up" and speeds back up to 60mph.

It only does it if the speed is set below 65mph. Set it at 70, it'll happily cruise along all day.

[mikeB]

It only does it if the speed is set below 65mph. Set it at 70, it'll happily cruise along all day.
[/quote]

Thanks for the tip. I'll give that a try, but I do try to maximise fuel economy and 60 is a good speed for that and 70 pushes consumption up quite a bit.

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I'd say either your motorised TB is out of range (ie; worn tracks) or there are issues with one of the sensors (this includes the feeds to/from them). Have you put it on a Lexia or Diag to see what it says?

The car is currently in France so I do not have access for 10 days. In the meantime could you give more info on "motorised TB". I do have Lexia but that is here in Bury. I'll connect up when I get the car back. Thanks for your advice.

[addo]

The drive by wire throttle body; Lexia will show you at idle what voltages are being applied whilst telling you the ideal voltage range. A consistent mismatch implies wear to the unit.

[mikeB]

The drive by wire throttle body; Lexia will show you at idle what voltages are being applied whilst telling you the ideal voltage range. A consistent mismatch implies wear to the unit.

Thanks. Now it seems a bit clearer. I have also noticed that when the CC is engaged and speed starts to decline if I press the accelerator, even by a tiny amount, the speed immediately starts to increase up to the set speed. I will check all this when I get the car back.

[mikep1973]

Today I drove 212 units of distance.

First 90 or so were on very quiet early morning road. I set the cruise to 90 and just went along happily for an hour or more. Perfect.

Second part had traffic. Set cruise to 65. Kept losing speed, as much as 15mph before waking up again and going back to 65.

Odd.

Sent from my GT-I9300 using Tapatalk 2

[mikep1973]

Today I drove 212 units of distance.

First 90 or so were on very quiet early morning road. I set the cruise to 90 and just went along happily for an hour or more. Perfect.

Second part had traffic. Set cruise to 65. Kept losing speed, as much as 15mph before waking up again and going back to 65.

Odd.

Sent from my GT-I9300 using Tapatalk 2

Ok, just to throw this into the mix.

Yesterday I fitted a TDI-Tuning box.

Cruise now works perfectly. Sits at 60mph when commanded, doesn't loose any speed at all. Sits at 55, 50 - exactly as it should work.

I am not sure why this is.

I did remark on this some time ago last time it had a tuning box fitted, but I thought it was an anomaly. It's not. With the box fitted, it works perfectly.

Must a "bug" in the ECU programming. I don't believe any M59 was ever fitted with cruise as standard.

[mikeB]

Hmm. Could you give a bit more info on the TDI tuning box. What does it do, what advantages, easy to fit? And what cost. Thanks