S4-2004, I think that throttle problem is *real*.
11-12-2003, 09:04 AM
#21
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I believe this can happen in any manual transmission if your rev matching is off while downshifting
especially if driving slow and you over estimate the necessary revs needed in order to match your gear shift
11-12-2003, 09:05 AM
#22
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I work on ETC systems, maybe I can help...
Since I work on ETC (Electronic Throttle Control) systems for a major automotive supplier here in Detroit, maybe I can help you out with this problem. Although I have only been working a year out of college, I have picked up quite a bit from our ETC team. Just so you know, I own a 2003 Jetta and it has ETC issues that I have found. I think that the perceived issues are common among all VW/Audi brands. Since I haven't kept up the history on the new S4, what kind of problems are you seeing?
It sounds as though one of the problems you are seeing is sometimes when you stomp on it, the engine pulls much harder than other times. This is something I noticed on my Jetta. One of your ideas was to test throttle position vs. pedal position. I can tell you that it probably won't tell you anything. Ok, time for some transfering of knowledge from what I have learned this year on ETC systems... If the ETC strategy (meaning the software strategy) is an open loop system, then there should be a direct relationship between pedal position and throttle position. This means I push 'x' amount on the pedal, I get 'x' degrees throttle position. Open-loop systems mean there is no feedback (or at least it doesn't modify the throttle position) from spark, fuel, or air sensors so they don't affect throttle position. More than likely, the VW/Audi ETC system is not this kind. This was sort of the "first" generation ETC systems. They are still used today, but usually only for very low cost ETC systems.
The second type of ETC system is called a "closed-loop" system. This means you push 'x' amount on the pedal and the ECU (electronic control unit, or the computer for short) calculates a throttle angle that can be influenced based on the feedback that the ECU is receiving form its fuel, spark, and air sensors.
What you would need to understand to figure out this problem, is when you stomp on the pedal ( called going to WOT, wide-open throttle), how does the software strategy use its feedback to adjust throttle position. Also, some ETC systems are torque based meaning when you press 'x' amount on the pedal, the ECU calculates a "desired torque." Open-loop and closed-loop systems can be this type. If that is the case, you can imagine that if for instance, the transmission was underdesigned and was only recommended for 250lb-ft of torque, the ECU would try to limit the engine to a maximum of 250lb-ft. Actually, we limit torque in our strategy so that huge changes in torque (such as downshifting and going to WOT) are easier on the transmission even if it wasn't underdesigned. We also limit torque for traction control purposes.
So long story short is, unless you understand the software strategy (which I'm guessing is on the order of about 10,000 lines of code) you won't be able to figure out why sometimes you get more power than other times. It is a very large and complicated system that I know the service shop in the dealers could never solve. If you have any more questions, I'll try to answer them.
It sounds as though one of the problems you are seeing is sometimes when you stomp on it, the engine pulls much harder than other times. This is something I noticed on my Jetta. One of your ideas was to test throttle position vs. pedal position. I can tell you that it probably won't tell you anything. Ok, time for some transfering of knowledge from what I have learned this year on ETC systems... If the ETC strategy (meaning the software strategy) is an open loop system, then there should be a direct relationship between pedal position and throttle position. This means I push 'x' amount on the pedal, I get 'x' degrees throttle position. Open-loop systems mean there is no feedback (or at least it doesn't modify the throttle position) from spark, fuel, or air sensors so they don't affect throttle position. More than likely, the VW/Audi ETC system is not this kind. This was sort of the "first" generation ETC systems. They are still used today, but usually only for very low cost ETC systems.
The second type of ETC system is called a "closed-loop" system. This means you push 'x' amount on the pedal and the ECU (electronic control unit, or the computer for short) calculates a throttle angle that can be influenced based on the feedback that the ECU is receiving form its fuel, spark, and air sensors.
What you would need to understand to figure out this problem, is when you stomp on the pedal ( called going to WOT, wide-open throttle), how does the software strategy use its feedback to adjust throttle position. Also, some ETC systems are torque based meaning when you press 'x' amount on the pedal, the ECU calculates a "desired torque." Open-loop and closed-loop systems can be this type. If that is the case, you can imagine that if for instance, the transmission was underdesigned and was only recommended for 250lb-ft of torque, the ECU would try to limit the engine to a maximum of 250lb-ft. Actually, we limit torque in our strategy so that huge changes in torque (such as downshifting and going to WOT) are easier on the transmission even if it wasn't underdesigned. We also limit torque for traction control purposes.
So long story short is, unless you understand the software strategy (which I'm guessing is on the order of about 10,000 lines of code) you won't be able to figure out why sometimes you get more power than other times. It is a very large and complicated system that I know the service shop in the dealers could never solve. If you have any more questions, I'll try to answer them.
11-12-2003, 09:46 AM
#25
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This can happen but it's not the case here...
then the symptom I described also happens when rev is matching exactly! If I where not able to match the rev I would not post it :-)
The feeling is like you would stay at the throttle position even if you lift your foot!
The feeling is like you would stay at the throttle position even if you lift your foot!
11-12-2003, 09:58 AM
#26
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I've noticed that the rpms seem to hang when shifting...
this didn't happen when i first drove the car, but I figured it was adapting to my shifting style. At first they would drop very quickly, resulting in quicker shifts. Now, the rpms hang a bit when I shift, allowing me to coast through the gears.
It's almost as if the exhaust has something to do with it, because I got a similair hanging rpm effect when I put a free-flow exhaust on my B5. The rpms would slow down and not drop as fast as with the restrictive exhaust. :-/
It's almost as if the exhaust has something to do with it, because I got a similair hanging rpm effect when I put a free-flow exhaust on my B5. The rpms would slow down and not drop as fast as with the restrictive exhaust. :-/
11-12-2003, 10:31 AM
#27
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You did say you're not sure if it has "something to do with the timing of shifting, clutch..."
That's the only reason why I suggested it might be that your matching is off. I did not realize you were referring to the computer's timing. I also double/clutch and rev match and have found that I have to work a little harder to get nice smooth shifts. But although I have found the learning curve to be a bit steeper I am adapting to the car and achieving smooth shifts naturally and reflexively. Maybe you need to anticipate that lag in deceleration after blipping it when you double-clutch/rev match? But if this is a signifigant and very apparent lag then maybe it is faulty mechanics.
11-12-2003, 11:21 AM
#30
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No, you've misread me slightly
I'm not saying they wanted it to be unpredictable. I'm saying they had other agendas, such as wanting to temper the impact of the harshness of rapid throttle position changes to the engine, and that they decided that the unpredictability that it generated was "acceptable."
I'm also suggesting that it is not the same from one car to the next, and that there may actually be a flaw in some aspect of the system that makes it worse for some of us than others. I'm suggesting that AG might not consider these cases acceptable, but AoA probably has no clue that such a concern even exists. With 15 broken transmissions and all the other problems, is it so hard to believe that the DBW throttle system is also experiencing a production-line variance?
No, it's easy enough to beleive. But it is going to be harder to diagnose because it doesn't *seem* very important on the face of it.
And I wouldn't lead with a threat ever. I'm only pointing out that if addressing it positively and cooperatively fails, there is more leverage to be had.
Many of you have commented that you've gotten used to it, and when you miss a shift, you know what you did wrong. Well, there are two potential explanations of that: yours is predictable, where mine is not, or 2) yours is also unpredictable, just on a significantly lower frequency than mine.
I'm also suggesting that it is not the same from one car to the next, and that there may actually be a flaw in some aspect of the system that makes it worse for some of us than others. I'm suggesting that AG might not consider these cases acceptable, but AoA probably has no clue that such a concern even exists. With 15 broken transmissions and all the other problems, is it so hard to believe that the DBW throttle system is also experiencing a production-line variance?
No, it's easy enough to beleive. But it is going to be harder to diagnose because it doesn't *seem* very important on the face of it.
And I wouldn't lead with a threat ever. I'm only pointing out that if addressing it positively and cooperatively fails, there is more leverage to be had.
Many of you have commented that you've gotten used to it, and when you miss a shift, you know what you did wrong. Well, there are two potential explanations of that: yours is predictable, where mine is not, or 2) yours is also unpredictable, just on a significantly lower frequency than mine.