"Limp Home Mode" when giving it welly?

**constablechris** · 23-03-2009,04:54 PM

Hi,

I've done searches on the forums for this problem, but a variety of solutions and variations to the problem were thrown up so I thought it best to start a new topic and explain my problem.

Sometimes (not all of the time) if you take the car over 3,000rpm with heavy acceleration, it will feel like you hit a brick wall and stop accelerating/accellerate very slowly.

This is generally in 3rd and 4th gear. I can't remember if it's happened in 2nd.

But once it's hit this 'brick wall' of power loss, it remains very power limited.

If you pull to a stop and pull away, it is drastically down on power through all gears.

But if you turn the engine off and start it immediately again, everything is back to normal and the power is all back as it should be.

There are no warning lights on the dashboard that illuminate when the car loses power.

An OBDII reader shows no codes, but I understand they wont show anything manufacturer specific.

Is this likely to be the MAF sensor? i've been quoted £173 to get a new one.

Thanks

Chris

**Mr V** · 23-03-2009,09:41 PM

I had a similar fault with a 3.0 TDI and believe it or not it actually turned out to be the fuel filter that caused the fault.

**constablechris** · 23-03-2009,10:23 PM

So can a variety of faults cause the car to enter this low power mode?

I'm suprised there is no light on the dash to tell you.

I forgot to say, mines an A4 1.9TDi - 110 variant. 1997 on an R plate, 119,000 miles.

**thorpyuk** · 24-03-2009,11:38 AM

Hi Chris, i have exactly the same issue, with almost the same car. (110TDI 1998)

Couple of things -

1) £173 for a MAF sensor is a laugh - i paid £53, and this included a £25 refund for returning my old one, and it was a genuine bosch part from gsfcarparts.com - i live in north birmingham, so there's one not far away.

2) The MAF did not sort the problem out, and i've tried also replacing the MAP sensor, all the vacuum hoses and the fuel return lines, but to no avail.

3) I'm beginning to suspect that the turbo VNT mechanism is sticking, but i'm not a mechanic and cant get the turbo off to take a good look at it!

If the guy above suggested that swapping the fuel filter sorted his problem out, that's the next thing i am going to get done!

**constablechris** · 24-03-2009,12:36 PM

Mine had a fuel filter done relatively recently, so I'd be surprised if that was the problem here - but give it a go and let me know what happens!!

Have you had yours plugged in to a computer to see what it says?

**thorpyuk** · 24-03-2009,01:53 PM

Originally Posted by constablechris

Mine had a fuel filter done relatively recently, so I'd be surprised if that was the problem here - but give it a go and let me know what happens!!

Have you had yours plugged in to a computer to see what it says?

No havent had chance yet.... i'll let you know how it goes :s

**Alan02** · 24-03-2009,02:07 PM

Hi, An `Over boost` condition can cause a Limp-Mode fault also.Not sure on the turbo on this model,but if its variable vane,then they can stick/jam on full boost and the engine management backs-off the fuel to protect the engine.Stop and turn ignition off, and system re-sets.Just a possibility.

**constablechris** · 25-03-2009,01:40 PM

Hi Alan02,

OK - sounds like it might be something like that if not the MAF sensor - is there any way to diagnose this?

Also, you mention the turbo vanes stick - I thought about this and figured I very rarely take my car over 3,000 rpm as the torque is good enough below this not to have too during all but the most progressive styles of driving.

If they stick, would consistently taking the engine over 3,000rpm to get the turbo going do anything "unstick" the turbo and help the problem remedy itself?

Thanks

Chris

**constablechris** · 25-03-2009,01:41 PM

I'm not entirely sure on the turbo type either - all I can tell you is that it's a 1997 on an R plate, and the 110Bhp/81kw variant. It's red too! ;-)

**Alan02** · 25-03-2009,02:09 PM

Hi Chris,i forgot to mention that if there was insufficient boost it can cause this fault also,as the system would be injecting lots of fuel depending on throttle position and it would sence no boost to deal with the extra fuel injected.Check also,vacuum hoses to the egr and turbo sensor,and also wiring plugs.Check the vacuum hose to the turbo too.Hope this helps,good luck!