Unintended acceleration problem on 1.4tdi 75 2004 A2

T

tomhasana2

New Member
Hi all,

I purchased a 1.4tdi 75 A2 (2004) in August last year, and since purchase it has had a problem with unintended acceleration which I wonder if you may have any ideas on?

The car drives okay below 2,000rpm and under moderate acceleration everything is okay. But when pushed hard into boost around 3,000rpm, when releasing the accelerator pedal, the engine will continue to accelerate on its own in most gears (but not 1st gear).

Sometimes this acceleration is very jerky on/off (especially noticeable in 3rd gear), if in 5th gear it will just continue to drive as though it has some mysterious cruise control for 300 yards or so before then shutting off the fuel and engine braking (there is no cruise control on this car).
Sometimes when clutch is pushed in when this happens, the acceleration will climb for 500rpm further, then go back to idle.
Sometimes if revs are high, around 4,000rpm and clutch pushed in, the revs will just climb to redline and hold there.
Occasionally the car will also accelerate itself below 2,000rpm but this is less often.

I have found that when the car accelerates on its own, braking when in gear will eventually stop the acceleration.

The car idles perfectly, and when this acceleration issue isn't happening, it will drive exactly as a 75 should.

The car is showing a realtime MPG reading when the unintended acceleration is happening.

The car has 155,000 and I don't believe anything other than standard servicing has been carried out.

Any ideas on what you think may be causing this would be greatly appreciated.

It has been smoke tested at Stealth Racing and no leaks noticed (but doesn't necessarily mean there aren't any tiny leaks that can't be seen).
I have replaced the N75 vacuum solenoid but this did nothing to improve the issue.

Thanks in advance for any replies.

All the best,

Tom (has an A2)
 
Probably best to start with a scan of the car to see if there are any fault codes logged. It could simply be a faulty accelerator pedal module, but needs further investigation. I'd be wary of driving it with this fault.
 
Howey said:
Is the oil level correct?
Does it use oil?
Click to expand...
I think @Howey could be on the right track here. It sounds like the engine is starting to run away on its own oil.

Is the dipstick end broken off? This is a common issue, but if you don't realise what's happened you think the level is below the end of the dipstick, which is now rather shorter as a result, causing you to overfill the oil and risking runaway. I would be surprised if Stealth hadn't spotted that though.
 
Or the ASV is not working correctly - missing gear tooth or oil filled controller. Assuming it is a BHC engined car.
 
Very odd the dis screen changes to mpg when it happens, do you have a 75bhp tdi with a dis or colour mfs screen then? Does the screen change from what ever setting its on to mpg when it happens without fail everytime? 🤔
This would indicate something other than just a mechanical error.
Come back with some more info, this is very unusual
 
Thanks for your replies

"Probably best to start with a scan of the car to see if there are any fault codes logged. It could simply be a faulty accelerator pedal module, but needs further investigation. I'd be wary of driving it with this fault."

Vince at Stealth drove the car with laptop plugged in and confirmed that the accelerator is showing as completely "off" when not being pressed.

Car has been scanned and showed no faults originally, but at one time it did give an oil level sensor reading which was cleared and has not occurred again. I had thought this sensor was changed by Stealth but will ask to confirm as it may have been missed off when serviced last.

Is the oil level correct?
Just checked and it looks a little high on the dipstick

Does it use oil?
It doesn't seem to use any oil at all

Is the dipstick end broken off?
I think it's all there, picture attached showing dipstick with (high) oil level

ASV is not working correctly - missing gear tooth or oil filled controller
This is interesting, and something I will ask to check next time at Stealth

It's a normal red coloured screen with DIS, the screen doesn't change itself onto the mpg setting automatically, but it does give a mpg reading (if the mpg screen is selected) when this problem is happening. Is it possible the car would give a mpg reading if it were to be burning oil?

Thanks again for your help with this

Tom
 

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I would ignore the dis then thats a red herring. Concentrate on the asv throttle controller, and oil level needs to be certain then monitored closely..
 
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