Strange cruise control issue
 

So since I bought my '06 3,0tdi a couple of weeks ago, I've noticed the cruise control is sometimes misbehaving...

Say I'm going along at 100kph, when the terrain varies slightly, sometimes the speed starts dropping. Slowly, slowly, down to maybe 90 or even 80kph. Then suddenly it seems the car discovers the speed is wrong, shifts down two gears and floors the throttle to get back to speed.

Other times the car keeps the set speed just fine within 3-4kph, no matter what hills or corners it encounters.

Only fault codes present are broken solenoids of both transmission mounts..

Any ideas ?

Strange one that, was the road rough and did you have any traction control lights on?

Only thing I can think off is the body acceleration sensors are telling the car that it not appropriate to accelerate.

I notice mine won't speed up if cornering but once on the straight again it does

No lights that I have seen, and the roads I've driven when this has happened haven't been rough at all..

Since the deceleration is really slow, it's almost like the throttle locks up at say 10%, when the change of the road means it needs 15% to keep the speed up.. From 100 down to 80-85kph could take like 10sec or something..

If I manually push the throttle then everything is fine and the speed increases, so I guess ESP/tc has no issues.

Is there any tb adaption that could be wrong like petrol engines have ?

Yes I'm with Del never heard of that one but some thoughts
If you press esp button to disable traction does it still do it
Are all the tyres of similar wear ...... thinking slight miss match on rolling circumferences on wheels .

Had a 5 series bmw few years back that would not always go into top gear and engage converter lock up and also would drop speed on cruise control and then pick back up ...... it happened when owner replaced rear tyres only

The fix was replacing front tyres aswell !

Problem is when I engage cruise control the ESP enables automatically :(

Drove around for about an hour tonight and didn't get the issue once.. Other days it happens more often, so it's not easy to figure out..

Right you are ,it auto enables traction for safety , if you get a spell were its playing up see if putting it in sport mode changes anything ..... worth a try ??

Silly question - I think we're all presuming you have regular cruise control, not adaptive cruise control - Can you confirm ?

I like where your thinking is going, with a potentially hilarious answer to this issue

It would be a ridiculously simple answer to an otherwise quite perplexing issue !