More power when easing throttle

[gman1981]

Hi all,

Someone else had had this problem recently, but I can't for the life of me find the post.

Basically, if I'm putting my boot down, as I ease off the accelarator, the car feels like it has even more power and accelarates even harder until the peddal is released that little bit further.

It isn't dangerous or anything like that, it just seems that the car has more power on part throttle, rather than on full throttle.

Any ideas?

Cheers
Graham

 

[1animal1]

i think it was tufty who had this...although i have been wrong before

 

[Mr.G]

MAF related I'm sure. Tuffty will be along soon no doubt.

G

 

[<tuffty/>]

I have experienced this but not looked into it yet... difficult to diagnose without logging at the same time and inevitably I am not doing that when it happens... not happened to me for a while but it may well have something to do with the control that the ECU still has over the throttle body... you may think you are in control but the ECU really is...

One theory I have is that as you let off the throttle a little the closing of the throttle speeds the intake velocity a bit given a kind of 'turbo boost' (ironically) as I haven't lifted off enough to create a vacuum and thus opening the DV to vent boost pressure but I attributed this to the fact I have a larger turbo and so there is more boost pressure and air volume there anyway compared to a stage 1 mapped K03/K04 turbo'd car...

Once I have my power baselined and everything checks out ok when run up on Bill's dyno I will try and revisit this...

<tuffty/>

 

[Welly]

I have experienced this but not looked into it yet... difficult to diagnose without logging at the same time and inevitably I am not doing that when it happens... not happened to me for a while but it may well have something to do with the control that the ECU still has over the throttle body... you may think you are in control but the ECU really is...

One theory I have is that as you let off the throttle a little the closing of the throttle speeds the intake velocity a bit given a kind of 'turbo boost' (ironically) as I haven't lifted off enough to create a vacuum and thus opening the DV to vent boost pressure but I attributed this to the fact I have a larger turbo and so there is more boost pressure and air volume there anyway compared to a stage 1 mapped K03/K04 turbo'd car...

Once I have my power baselined and everything checks out ok when run up on Bill's dyno I will try and revisit this...

<tuffty/>

Venturi effect for those interested.

http://en.wikipedia.org/wiki/Venturi_effect

I had this when using an air filter with a small hole for connecting to the MAF. The hole was in fact smaller than the MAF, meaning that the air sped up to get through the smaller hole, thus giving me higher MAF readings.

The above gave me MAF readings of 220+ g/s. Only realised what was going on when a new filter was fitting, dropping the air flow down to the correct value.

 

[gman1981]

it seems a lot more noticable in higher gears if that helps.

 

[Matt82]

i drove a couple S4s with symptoms like this. i put it down to MAF not being able to correctly "count all the airs" coming in at WOT so didnt make "full bean"

when you backed of the throttle, less air flowed, the MAF made a better sense of the lesser air flow, and so made more beans

 

[mark_sarah]

Mmmmmm. This all sounds interesting.
I have recently noticed this on my S3 exactly as you describe. It feels like its boosting when you take your foot off the accelerator, after giving it a foot full.
I have only noticed this since i replaced my air filter, with a pipercross panel filter. And my MAF started playing up, but seemed to be rectified when i cleaned it.

I have put the fault down to a faulty MAF, but not going to change it until it dies completely.

But sounds like it could be related to the air filter change as well.

 

[MintyS3]

I have this too. Before and after replacing the maf.

 

[vetch]

Yep, Ive experienced this from day one of ownership.

 

[Matt82]

what does vagcom say your throttle position sensor reports?

 

[Felixo]

And I thought I was special if not blessed.. Damn MAFia :-]

 

[5ean]

I have this also.. Gonna give the MAF a clean at some point, if that dont cure it i will just replace it.. Knowing my luck the problem will still be there but hopefully not.

 

[mark_sarah]

Are you all running standard filters? I noticed it more when i changed to the pipercross panel filter, wondered if this could be related!

 

[5ean]

I just had a full service last month and its a standard filter thats in..

 

[gman1981]

after driving it for 3 hours on the motoway yesterday, I noticed that it is actually quicker on part throttle. This means that as you back off from full throttle, you pass the "part throttle" stage where I have the most power.

Is this the same problem a lot of you seem to have?

 

[Nyteryda]

yup, its the same on mine.. would love to know what needs to be done to get that power on full throttle !!

 

[mark_sarah]

I've noticed in the last couple of days, that if i turn the traction control off it is'nt as bad. When i say it is'nt as bad, i mean i only noticed it 5% of the time with the traction control turned off, compared to 60% of the time with it turned on..

Anyone else noticed this?
Is there a throttle sensor? If there is, is it possible this is the problem?

 

[fran-s3]

randomly I had this when my fuel pump was failing... easing it in was fine but as soon as I gave it full beans it hesitated and spluttered (which aps diagnosed as actually misfiring). The fuel pump couldn't deliver the fuel at full load as it was broken hence why my car was hesitating as it wasn't getting enough... but slowy accelerating was fine, weird.

 

[sportstractor]

oh dear, now everybody is going to go changing there maf and fuel pumps. id start with cleaning throttle body and alignment. Suprising that didnt trigger a warning light fran

 

[brys3]

could a knackered lambda sensor cause a similar issue due to possibly over fueling when you stomp the pedal to the carpet?

 

[mark_sarah]

Update to this problem i share with gman1981.

In the last 2 days it has got a lot worse all of a sudden, today i thought i would try driving to work and back with the MAF unplugged. The car then ran fine, just under powered, which i would expect with the MAF unplugged.

Would you say that makes it conclusive? I need a new MAF......

 

[sportstractor]

if it runs better with a new maf, then maf is the problem. I believe the ECU runs on preset values when the maf is unplugged

 

[mark_sarah]

Mine is now running fine after i changed the screws for my air box top.

I noticed yesterday when giving my car the once over, that one of the screws that hold the top of the air box down was slipping and not tightening, which meant the air box was not 100% sealed. I removed both the screws and replaced them with self tapping screws which were 10mm longer.

I can't see how this would of caused the flat spot when on full throttle, but it certainly got rid of my issue, and all for the price of 99p.

Worth a look i think......

 

[Matt82]

i had this problem last friday (i pull the car apart quite regularly at the minute for development..)

more beans on part throttle

more work was carried out on sunday and i gave some clips the once over

long and short of it, i blame the "better part throttle response" thing on boost leak.