PD130 Juddering and Cruise Cutting Out

[Jamiem]

Morning, the cars done 191k and he been good as gold for the past 80k or so with no problems what so ever. I've serviced it religiously, and always maintained it regardless. On Saturday I had 2 new tyres fitted, then drove home and parked up til this morning. I've just driven the 35 miles down the motorway to work and the first indication that something was wrong was when it cutting out the cruise control. It would judder a couple of times, then start slowing down. It cruises just fine on normal throttle pedal inputs. I then noticed that it's putting it's own throttle input in when off the throttle and slowing down, as proven by the instantaneous mpg display fluctuating around 140mpg when normally on slow down it would be - - -. Any ideas what's going on? I'm going to do a vcds scan this evening, but the only thing that springs to mind is perhaps one of the front abs sensors has been disturbed (but no warning lights of any kind on the dash) .

Cheers
Jamie

[Jamiem]

ABS sensors pushed home as they should be, so I'll see if a scan shows anything as it's still giving throttle when it shouldn't and fuel economy is non existent!

[Jamiem]

No fault codes, clutch and brake pedal switches show as working fine too. I guess I'm going to have to do some logging, any clues as to what to watch? I was going to do one run logging abs sensors, another logging throttle position and maf? any others to watch for? What sort of figures should I see from the MAF? The car was remapped about 4 years ago if that makes any odds as to what I'll see on the log.

[Pickard1]

It might not be any use, but my car was juddering and loosing power and it turned out to be the injector wiring loom, which I believe is fairly common. (common enough that the dealers have it in as a stock item!)
My car is a PD130 and had done about 150,000 when this happened.

[Jamiem]

Hi, thanks for your help but I know it's not that, I had that one a couple of years back so know the symptoms and this is nothing like it. The easiest way to describe it is as if you kept jabbing your foot on the accelerator while coasting down a hill. It's actually accelerating rather than misfiring or losing power.

I used vans yesterday and all abs sensors stay in sync up to 20mph when it logs you out of the abs controller (for safety I guess), the clutch and brake sensors are working as they should, the throttle pedal input is stay and doesn't do anything odd and still no fault codes so I really am at a loss. The lady resort is to unplug the clutch sensor as it drives perfectly then, but this means no cruise control which will be a pain driving 80 miles a day!

[Jamiem]

Final update:

About 3 weeks back it fixed itself, CC was working fine, no juddering, all exactly as it should be. Great I thought. Then last Saturday while coming down the motorway I lost throttle control, a quick off/on cycle and all was ok, but it would surge if I tried to engage CC. over the course of an hour it went from iffy to dead. I got towed the final 20 miles home by the AA and knew what it would be. A quick VCDS scan confirmed a dead pedal, again. It happened around 4 years/90k miles ago last time, and this little blip was exactly the same as last time. VW wanted almost £90 for a new one, so on ebay I go and order a used one from a breakers for £15. Fitted tuesday and all is perfect again.

So in summary it would seem that the earlier surging was an early indicator that the pedal was knackered, and although the live data initially showed no faults, upon the last scan it showed throttle hovering around 1.6-2% when not touching it.