I ain't got nuthin'


#1

I own a 2004 Audi A4 1.8T. I am experiencing a problem with my acceleration pedal where in certain situations I ain’t got nuthin! What I mean is this…typically after the accelerator has been depressed and the situation calls for the car to roll up to a yield sign or a stop sign or when coming to a complete stop…then depressing the accelerator to re-accelerate into traffic or to get rolling…this is when I get nothing. “Nothing” in this situation means the car doesn’t accelerate, doesn’t rev the engine (no change in rpm)as it would if it were in neutral, it doesn’t do anything…then typically after a few second delay it will accelerate. This is not only frustrating, but at times it is dangerous because I might be counting on the acceleration to keep me out of harms way. Last week I took it in to get fixed. I was told it was the throttle body. I paid to have it replaced. This repair cost me $800 and it behaves the same way still…in fact it occurs more frequently. What’s up with this? Any other Audi A4 owners out there that have experienced this? Any suggestions? In my opinion, the problem wasn’t the throttle body since it is still happening…


#2

It could be the controller that operates the throttle because it may not be a direct connection to the gas pedal. It coud be a computer problem which may be covered for longer than the basic warranty because it is a smog system part.


#3

the throttle body and motor that actuates it,are ‘drive by wire’,as in controlled by computer-no throttle cable like in the old days.your car’s computer hasn’t lit up the check engine light,yet?i’d take it back,if they hook it up to a diagnostic computer while actually driving it,they might get a better idea of what’s malfunctioning.


#4

Audi has a Technical Service Bulletin (TSB) dated Feb. 27, 2007 #01 07 03 which covers this situation. According to the TSB, the problem is driver induced.
The Audi has a system called Electronic Power Control (EPC) which is a “drive-by-wire” (electrical wire signal) system. When the gas pedal is depressed, a signal is sent to the engine throttle. There is no mechanical connection between the gas pedal and the engine throttle.
When the gas pedal is depressed, and the brake pedal is simultaneously depressed, the engine will stay at idle rpm. Take your foot off the gas, and the car will go.
Have someone to observe your driving to monitor your foot positions. They report whether the problem occurred even when your left foot was off the brake pedal, or not. If your foot was off, and the problem occurred, that would indicate a control problem.
If the control computer acts on a signal from the brake pedal switch, the brake pedal switch (if it is the signal to the computer) could be out of adjustment, or faulty.


#5

Thanks very much for taking the time to respond to this. I learned how to drive with my right foot only so it couldn’t be driver induced (since there is no physical way that both the gas pedal and the brake pedal could be simultaneously depressed)…its kind of an inside joke in my family because my father drove with two feet and we used to kid him about it to his annoyance…do you still think it could be related to the brake pedal switch anyway?..Thanks again.


#6

thanks very much…i’ll pass on your advice


#7

thanks for this…the basic warranty period is over…but i’ll double check the policy for smog system part applicability…


#8

There is a performance driving technique, called “heel and toeing”, where the driver does use one foot to depress both the gas pedal and the brake pedal, simultaneously.
Since many driving (body) movements are done subconsciously, you STILL need an independent observer to make the report on your foot movements.
There is some switch which tells the engine control computers when the brake pedal is depressed. You need the repair manual, tools, know-how, or a knowledgeable mechanic to check it out.
It’s possible that the throttle is hanging up—either the throttle plate, or, its actuating mechanism. Anyway, the system, including the driver, need to be checked out.
One can only wonder when “drive-by-wire” brakes and steering will come into use.


#9

I was just out to pickup my daughter from an appointment…I asked her to observe…its not me…my heel stays in contact with the floor and my toe switches from the brake to the accelerator, however, I think you are onto something as to a connection between the brakes and the accelerator…what I just observed is more like a delay or down period (like the brain/computer/electronics is too slow and needs too much time to think about changing from braking to accelerating)…eventually it does recover and accelerate but there is a delay


#10

Maybe your brake switch is slow to release. Get someone to watch behind the car (or set up a mirror) and see if the brake lights go off as soon as you lift your foot from the brake pedal. (This assumes that the computer is monitoring the brake light switch, and not some brake fluid pressure switch.)


#11

FYI on the Electronic Throttle Control (“drive-by-wire”). That sensing element is a dual potentiometer ----- not, brake switch. Click, and become learned: http://autospeed.com/cms/A_108379/article.html

Added: To clarify, the dual potentiometer is attached to the gas pedal.


#12

Okay buddy, enlighten me. I have throttle by wire on both of my cars, and I am well aware of the redundant potentiometers for gas pedal position sensing. I was clearly talking about the brakes applied safety sensing that this particular car has. Please point me to the exact line in the linked article that claims that this system uses potentiometers on the brake pedal!


#13

Tardis,
You’ll have to read the article for yourself. Besides, I was talking to rick. Perhaps, you know for a fact that the brake switch is incorporated into the throttle control system? I don’t know for sure, either way.
hellokit.
There is a part 2, to the article, in Issue 430. Issue 429 carries part 1. To go to part 2, In the search block, put the name of the article, add “part 2”, and click.


#14

Still no mention of brake on/off or position detection. The system does it, but the article does not bring it up. I have seen it done both ways (brake light switch or brake fluid pressure sensing switch), but I don’t know which this one uses? Do you?


#15

tardis and hellokit:
thanks very much again for your comments…btw- I checked the brake light timing as suggested and there doesn’t seem to be a delay. I’m taking the car to my preferred mechanic tomorrow (he was backed up last week and I felt I shouldn’t wait…last time I do that)…I will fill him in on all of this…if you have any more thoughts keepem’ coming.
Rick


#16

I got the exact same problem. i just took mine into the dealership, and they can’t find anything wrong or duplicate the occurrence. I’d love to know what happens on your end. I haven’t checked everything mentioned above, but that’s step 2.