When fitting a new accelerator/throttle pedal its two sensor values will not be the same as the previous pedal. How does the ECU adapt to the new values and range? Some automatic learning or do you have to adapt it somehow, manually or via VCDS?

Its just a twin track potentiometer, so should just be plug and play.

I know its just a twin track potentiometer moved by my foot, as is the throttlebody, except moved by a motor. You have to 'adapt' the throttlebody so the ECU learns which resistances (from G188 and G 187) represent 0% and 100% and it can extrapolate all points between.

I was asking by what process the ECU gets to know what resistances (from G79 and G185) and thus pedal positions represent 0% and 100% demand from the pedal?

It would be easy for the ECU if all pedals came with identical resistances for 0% and 100% but that is unlikely although not impossible. So I imagine the ECU does have to learn these values when a new pedal is fitted or as your old pedal wears over time. Does it 'adapt' itself somehow which seems likely? If so is there anything I can do to assist. Like reset the ECU so it looses all its learned values and knows it has to relearn.

 

I ask because having fitted a new pedal, idle under some circumstances has increased by 300rpm and I sometimes get a disconcerting feeling that the car accelerates itself slightly.

Edited 18 October, 20187 yr by LB123

3 minutes ago, LB123 said:

I know its just a twin track potentiometer moved by my foot, as is the throttlebody, except moved by a motor. You have to 'adapt' the throttlebody so the ECU learns which resistances (from G188 and G 187) represent 0% and 100% and it can extrapolate all points between.

I was asking by what process the ECU gets to know what resistances (from G79 and G185) and thus pedal positions represent 0% and 100% demand from the pedal?

It would be easy for the ECU if all pedals came with identical resistances for 0% and 100% but that is unlikely although not impossible. So I imagine the ECU does have to learn these values when a new pedal is fitted or as your old pedal wears over time. Does it 'adapt' itself somehow?

 

The pedal at rest will either be short or open circuit depending on the design.

I seem to remember @hutchysrs50 taking one of these pedals apart and posting some photos of the innards. I also faintly think I remember him mentioning adaptation?

Typically these arrangements have a 'padding' resistor in series with the tracks at each end.

 

It may be that adapting the TB simultaneously remembers the 'foot off pedal' resistances of the accelerator pedal pots?

I may have misremembered who dismantled a pedal, as I've just found this: https://www.briskoda.net/forums/topic/439709-replacing-throttle-pedal/?tab=comments#comment-4944228

 

Senior moment. Wasn't me. My evil twin causing trouble again.

Dementia symptoms, ask same question that you asked last year.

 

Why dont you try Throttle Body Alignment

 

 

Edited 18 October, 20187 yr by xman

No alignment or basic settings for the pedal itself, just fit it and plug it in, job done.

Did do a throttlebody alignment after I had fitted it. Thank you all for your replies and help.

8 hours ago, Wino said:

I may have misremembered who dismantled a pedal, as I've just found this: https://www.briskoda.net/forums/topic/439709-replacing-throttle-pedal/?tab=comments#comment-4944228

 

 

You remember correctly, I did indeed strip a pedal down and post up pictures showing the insides, your not over the hill just yet 

Problems continue. Car idles at about 750rpm. That's normal for this car. When slowing down to stop I tend to depress the clutch and press on the footbrake. For as long as I keep the brake pedal pressed the car idles at 1100rpm. Handbrake, clutch and car motion have no effect but a second after taking my foot off the brake pedal the idle drops to 750. I don't remember this before I changed the accelerator pedal and MAP. Normal or more weirdness from my car?

Faulty brake switch or leaky brake servo maybe

 

Edited 26 October, 20187 yr by xman

If I remember I'll try that on my car on the way out this morning, to check that this is not normal.

I do like @xman's idea about brake pedal switch, but that ought to throw a code?

 

Edit: no discernable effect on idle from brake pedal. Give it a scan.

Edited 27 October, 20187 yr by Wino

If this high idle is occurring when stopping, i.e. dynamically with car decelerating, rather than static, stood and pressing the brake pedal then it could simply be a split servo vacuum pipe which is pulling loose when the engine block leans under braking and moves back when the brake is released. Check the end at the inlet manifold.

 

Check the brake lights are working.

Edited 27 October, 20187 yr by xman

Brake lights working. Definite no leak in servo to manifold hose (repaired couple of weeks ago) and this car throws a fault code or four if there is the slightest intake air leak. No fault codes since replacing pedal and MAP two weeks ago.

Quote

no discernable effect on idle from brake pedal. Give it a scan.

Only idles high when slowing down with brake pedal depressed. It will stay idling high for as long as my foot stays on the pedal. I'm sure the ECU is telling it to idle at 1100 and the moment I take my foot off the brake pedal the ECU says 750 and the idle drops. I suspect it's an anti stall feature that has come into action. I think the ECU is doing it deliberately. It's completely repeatable, does it everytime I slow with foot on the pedal. Any speed. If I brake gently at 70 and slip it into neutral to coast revs settle at 1100 and stay there till I release the pedal.

To be honest it's not a problem in day to day driving and it can stay like that but it is a weird change in behaviour of the car.

Can't remember if you have VCDS, but somewhere in engine ECU measuring blocks you can view actual and specified idle speed, you could confirm your feeling that it is being actively demanded there with a bit of logging or a passenger to watch the screen.

 

The brake lights may still work even if the ECU part of the brake pedal switch isn't working, they use two separate switches.

Edited 27 October, 20187 yr by Wino

Good plan. Just find the idle speed the ECU is requesting. Did have a look in measuring blocks at the pedals and they show up as working normally.

Baby sitting at the moment so manana.

Edited 27 October, 20187 yr by LB123

Just because the brake lights are working does not mean the brake light switch is functioning correctly.

Solution.

Been a busy day and finally got round to solving four months of the high idle when slowing with clutch and brake depressed. Been to scrappy and got a replacement accelerator pedal. Fitted it and the cars idle has returned to 750rpm. Don't understand why the old pedal caused the problem but the 'new' pedal has sorted it. I was also getting slight hunting idle when starting from cold. That also hasn't happened although I've only done one cold start so far.