Lumpy and hesitant on light acceleration.

4.2 V8 32v Naturally Aspirated - 414 bhp
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Sonnyjim
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Lumpy and hesitant on light acceleration.

Post by Sonnyjim » Sun Feb 10, 2019 10:14 pm

I’m experiencing above problem until the car is fully up to temperature. I know they are a bit hesitant when cold but this is worse and only disappears when temperature hits 90 (engine not oil). It only seems to to be under light throttle, when I accelerate a bit harder it is smooth as normal.
It is very noticeable, to the point my wife returned with it after 10 mins thinking it was going to break down!

I had it out to the garage that does my servicing and the could find no faults but agreed it felt a bit hesitant.

Anyone else suffered similar?

Cheers

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MIDZ
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Location: Glasgow

Re: Lumpy and hesitant on light acceleration.

Post by MIDZ » Sun Feb 10, 2019 11:01 pm

I had similar a while ago, carried out vacuum test with vcds and it pointed to faulty airbox flap solenoid (not moving) everything thing else was slow to move. I blanked the vac hose going to AB solenoid with a golf tee and tested again. Now everything else was operating alot quicker. It was leaking vacuum pressure from solenoid and affecting everything else. Fitted new solenoid and fault went away

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12th
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Re: Lumpy and hesitant on light acceleration.

Post by 12th » Mon Feb 11, 2019 10:17 am

I had similar with the flaps in the inlet manifold. These were removed by MRC as part of an overhaul.
Sprint Blue B7 RS4 Saloon with MRC tweakery.

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FrazerD
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Re: Lumpy and hesitant on light acceleration.

Post by FrazerD » Mon Feb 11, 2019 1:36 pm

12th wrote:
Mon Feb 11, 2019 10:17 am
I had similar with the flaps in the inlet manifold. These were removed by MRC as part of an overhaul.
What are the purpose of the flaps? Would I be right in saying that they provide the shove at 5.5k? If so, can they not be opened like the exhaust flaps or do they have to be removed?

Cheers :thumbs:

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12th
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Re: Lumpy and hesitant on light acceleration.

Post by 12th » Mon Feb 11, 2019 5:08 pm

My understanding is that they smooth out the airflow, but if they get sticky as they wear (they are part plastic and part metal, I think, and cannot be replaced without buying a new manifold) but this goes as the engine warms up. If you remove them it doesn't seem to be quite so limo-smooth when treated gently and with low revs, but it's really a very small trade-off.

I think the shove at 5.5k is the engine map. I had a DMS one, followed by an MRC and they both made the engine far more linear across the rev range. MRC's map boasts of giving full throttle in the first three gears, so my belief (and it's nothing more than that) is that the standard map doesn't give full throttle in these gears unless you are above 5.5k. I may be wrong, but that's how it seems to me.
Sprint Blue B7 RS4 Saloon with MRC tweakery.

Sonnyjim
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Re: Lumpy and hesitant on light acceleration.

Post by Sonnyjim » Mon Feb 11, 2019 6:53 pm

Cheers for the replies. Will look into that next time it’s in for a service. Do the flaps not throw up a warning light if it’s out of position?

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12th
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Re: Lumpy and hesitant on light acceleration.

Post by 12th » Tue Feb 12, 2019 9:22 am

I'm not sure. If it does, this is addressed with MRC's remap. I doubt that you'll get an Audi dealer to remove them for you though - they will just suggest replacing the manifold.
Sprint Blue B7 RS4 Saloon with MRC tweakery.

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