gforcejim

I've got a 2002 A6 Quattro 4.2L which exhibits intermittent throttle response issues from a standing position through first and second gears. The way if feels is that the brakes are on with car hardly accelerating for the given throttle depression. An accompanying symptom is late shifting, meaning when you'd normally expect a 2000 or 2500 rpm shift for the given acceleration rate (slow) it may shift as high as 4000 or 4500 rpm, as if the engine were under a higher load.

I note that if during this I "pedal" the car, i.e. lift and return the throttle to its previous position, it surges ahead as if a load were removed and the car accelerates and shifts appropriately again.

I've had it in twice for this and they replaced the air flow sensor which had no effect. Then they "fiddled with some settings" to no effect. I am reluctant to send it in again as I am sensing they don't have a clue and aren't really driving the car to see if the problem is resolved before returning it.

As a race driver, I do tend to left foot brake so I wondered if perhaps my occasional and brief overlapping of brake and throttle (it would be very slight and instantaneous if I doing so--not extended for sure) might trigger some factory programmed acceleration override involving brake application. So I disabled the ESP using the dash button but the problem persisted. Recently I learned that this may not disable all functions so I pulled the fuses for the ESP (leaving the ABS fuse in). There are several, and when all are pulled the car will not even start, and behaves as if the spark plugs are out, i.e. cranks fast, easy and with no fire. I put them back one at a time and with one fuse in the car started with an ESP disabled light and an ABS light. So far, it seems that the problem may have gone away, but it is normally intermittent so it is hard to be sure as yet.

Does anyone have any insights on any factory programming to prevent or lessen acceleration if brake and throttle are used simultaneously? Does this involve the ESP/ABS systems? Of the several ESP fuses, which do what? Does anyone have any suggestions on what other conditions might cause this problem? I need to solve it and disabling everything but ABS is fine as I am highly trained to respond to a skid and these systems are not up to my responses and render the car's handling unpredictable (worse than nothing)to me.

georgeb944

Your brake pedal will override the accelerator pedal (remember the unintended acceleration lawsuits of the mid-1980s?).

That said, there is a way to blip shift under braking, either you brake then hit the accelerator or vice versa. I don't know how it works on a 4.2, but I have played with it in the snow on my 2.7T.

You might want to use VCDS to monitor/log the brake pedal input (to the engine computer) while you're driving and see if there is any correlation to the stumbling event.

gforcejim

Thanks very much, that's very helpful. I'll have the mechanic do that if possible. By the way, I should add that this is my family vehicle.

gforcejim

I now have confirmed that even with most fuses pulled I can provoke it with overlap of brake and gas from a full stop, no matter how instantaneous. So I'd like to repeat my earlier pointed questions, if anyone has specific information: Does anyone have any insights on any factory programming to prevent or lessen acceleration if brake and throttle are used simultaneously? How does this involve the ESP/ABS systems? Of the several ESP fuses, which do what? I need to solve it and disabling everything but ABS is fine as I am highly trained to respond to a skid and these systems are not up to my responses and render the car's handling unpredictable (worse than nothing)to me.

4Driver4

Any codes? Have you done a throttle body adaptation?
Start with the basics.

Airbag

<<<@!1!@>>>

gforcejim

In response to 4driver4 I haven't checked the codes yet, the only local source is one of the auto parts stores as the closest Audi dealer is an hour away and they don't seem to know what they are doing--I'm into this problem for $500 so far with a throttle body replacement, then they had the car for almost three weeks and I am convinced they didn't even look at it. I think they just want me to go away.

I will check the car today and post what I find. You're not dealing with an Audi tech person so I am not sure what you mean by a throttle body "adaptation."

Thank you for your input.

SloopJohnB@mac.com

You could try this:

Manual throttle body adaptation:

"The Throttle is "Drive By Wire" and adapts to your particular driving style. Do a TBA Throttle body adaption).

1. Get in your car, it doesn't matter if you close the door or not.

2. Turn the key to the on position, the position just before the starter turns over.

3. Press the gas pedal to the floor with the key in the "on" position.

4. Hold the pedal to the floor for five seconds, then turn the key back to the "off" position(don't remove the key), then release the gas pedal.

5. Wait 2 mins. for a full alignment. During this time you may hear very faint noises and clicks. I
only heard one sitting in my car, if I got out and popped the hood I might hear more.

6. Drive the car as you always do.

Depending on your driving style, this may or may not be a big factor. I do a lot of city driving so
I noticed a big change after erasing my history. It is not hard to do this, just follow the
instructions - Key on, pedal down, 5 sec, key off pedal up, wait 2 minutes.

Keep the key in for the entire thing. "

gforcejim

John,

Tried the Manual Throttle Body Adaptation procedure, and after a bit I deliberately overlapped brake and throttle from a standing start, albeit very briefly, I experienced the same problem. Extremely "soft" pedal response--like half to a fourth of expected power for a given throttle position--and late shifting, as in a given acceleration that might normally result in a 2500 rpm shift would actually shift at up to 4000 rpm. Pedaling the throttle during this would restore full throttle response and a shift.

I also checked the engine codes and got:

"Troubleshooting P0431
OEM Brand: Volkswagen

definition
aaWarm up catalyst efficiency below threshold-bank 2
Explanation
aaAir leak before catalytic converter
Probably cause
aa1.-Rich Air/Fuel ratio
aa2.-Faulty catalytic converter"

This is a recurring code, I have found and reset it before. The mechanic didn't find any leaks. The only solution offered was $1,200 cat replacement. Average gas mileage is in the mid to low 15mpg range and I was told this was not out of line. I do tend to drive a bit more aggressively than most people. So I declined to change it. Am I right in assuming this is not part of the problem?

Thanks for your help so far.

Just Me

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