wow... thats REALLY hard to get to. can you just unplug the wires, take out those two main screws, and the whole pedals comes off? itd be much easier to work on that way.

 

damn really? and i wanted to try another mod =P

 

That can't be why it works. I took mine out, and measured the resistance (and yes, I have a Fluke DVM, not some POS Radio Shack toy). Resistance changes instantly with even the very slightest movement. I also checked for any freeplay in the pedal/potentiometer. There is none. The pedal is spring loaded to return to full up, and the potentiometer is spring loaded to slam up hard against the pedal rod.

There are two carbon tracks inside the pot, and two completely separate circuits because it's redundant and the ECM checks both to be sure they agree. Mine give different values for the same position, but I am assuming the ECM already knows this.

So the curious question is, why can't I do the exact same thing by loosening the adjustment nuts and tweaking the position of the pot instead of sticking something on my throttle that could someday fall down and and do something I don't want?

Also, Toyco always puts adjustments in their manuals, but there is no mention of adjusting this pot, only complete assembly replacement. Why? Liability? Technical issue with field adjustments? (Not a rhetorical question, I really don't know why, and I'm really curious!)

Last, I am loathe to do this now since all my complaints about slow throttle left when I installed my Fidanza flywheel, and if I really, really wanted to do it, I'd remove the plastic stop and shim behind it to adjust it exactly where I wanted, or better still, move the thottle entirely to a different position where I could work it like a motorcycle and then I wouldn't have to heel/toe anything, but that would be a pretty radical change...

 

Yes. I takes all of a minute to remove if you are slow with the two bolts.

 

maybe the ecm doesn't change throttle position until a certain resistance is reached and that's what causes the freeplay. just because the potentiometer is changed resistance values with the slightest movement(every pot does this) doesn't mean that the ecm is reacting to that resistance value. there is probably freeplay programed into the ecu. and it's probably for safety reasons, since 15 years from now the pot probably won't have the exact same resistance values.

 

I would agree, except for one thing: since I installed my Fidanza flywheel, I have no delay at all. I have tested it repeatedly, and there is absolutely no hesitation from the slightest pressure.

I have some theories why this mod is doing what it does, but I can say for sure, if you reduce the inertia in the system, the perceived delay disappears.

 

Homebrew damper?? i wanna kno more about it...please tell me more

 

just did this myself with some electrical tape, going to measure with a caliper tomorrow and set a machine screw and bolts with some washers to do the same thing. will probably coat the top of the screw with silicone to prevent any tapping noises upon reaching the bump stop.

 

Just to clarify:

This mod should NOT increase your idle RPM. That is not the point of this mod.

Sean

 

Yes, you can do the same thing by adjusting the position of the pot, which I did.

However, I still think that the ECU is smart enough to compensate for variations in the adjustment of the switch. In fact, after I bumped my idle speed up to 800, where it idled smoothly, it has crept back down to the 650-700 rpm range. You can see this yourself if you simply push the pedal down a bit and hold it steady at 800-900 rpm. Over several seconds you will see the rpm slowly drop toward the standard idle speed. Then when you let off of the pedal, the engine speed will drop below the normal idle speed, and then work its way back up. It makes sense that the ECU knows what speed the engine ought to idle at (though I think the speed should be higher), and probably uses negative feedback to interpret a low, steady signal as the 'no throttle' position.

Having to adjust the position of the pedal pot to adjust idle speed would be the equivalent of an idle adjustment screw on a carburetor. Too primitive. If any permanent adjustment can be made, I suspect that it would be done by changing the ECU memory.

It could be possible that there is a 'threshold' value for the signal below which the ECU will not compensate for, as one member suggested, which could cause some dead travel in the pedal.

I admit that I'm speculating here. I'll try to test this further by adjusting the pot back the other way to see what effect it has on the engine speed.

Now, throttle delay should be defined for the purposes of this discussion. First, there is the delay from the time the pedal is depressed to the time that the throttle plate starts to open up (and the injectors start to spray more fuel, and the ignition timing changes, etc.). That is all that this pedal mod can hope to reduce. Then there is the time from when the throttle actually opens to the time that the engine reaches a corresponding increase in speed. This depends on several things, such as rotational inertia, intake runner volume and length, flow restrictions, etc. More physical changes are needed to affect this, like a lightweight flywheel.

 

Nice post. Good analysis!

I've observed the same thing about idle speed, and this engine has no IAC like a cable throttle does, so I think it's safe to assume that a large number of electromechanical processes are being done in the ECM software by controlling the throttle position directly instead of the old school methods using dash pots, motor actuated cable operated throttle control devices, idle air control valves, and the like. One of the first things I noticed under the hood of the tC was the relative lack of vacuum control lines. They've even done away with EGR valves because they can do the same thing with VVT. It really is a lot simpler under the hood, but far more complex in the ECM.

I bet you are correct about the re-evaluation the ECM does on the minimum throttle position. It sure does learn a lot of other things pretty quickly.

And I couldn't agree more about the throttle delay question. There are two separate issues: mechanical response to pedal change, and engine response to pedal change. The only thing I can say with certainty is reducing inertia worked wonders for me and the other four cars I've put a Fidanza flywheel in. I'd like to do even more.

I once had a 1200cc bike with a 24 lb crank in it. It revved like nothing I've ever had since. I've been a big believer in rotating weight control for a long, long time.

 

woa woa woa, this mod only works for manual?

 

One thing I've noticed with my car, is since the pedal has a good amount of initial resistance, it appears like there is a delay, unless you stomp on the pedal, but then full throttle has never been very responsive in the toyotas I've driven (I'm guessing the vvt-i has something to do with this -- like it's waiting a second to make sure you really mean it -- in order to save gas... total guess, but anyways...) I think in many cases the throttle lag is magnified by the fact that most people put their seat too far back. I used to be one of those people. That is, until I test drove a corvette and the sales guy told me I was sitting too far back... So I decided to take that advice with my car as well. It made all the difference for me. In fact, the car is a little *too* responsive sometimes. However, the mod in this thread seems like it works if you don't want to move your seat forward. :D

 

no it will work for an auto but what's the point? so that it's easier for you to match revs on a downshift?(sarcasm)

 

bah pointless mod IMHO just get a turbo or supercharger and make up for whatever slack you notice.

 

i think i'll try this mod this weekend...i'm used to the lag when shifting since i've had my car for over a year, but it'd be nice to get rid of it if i could. hopefully this works out.

 

i need to try this if i have that problem with my 06 TC

 

One possible explanation for the two strips in the pot is temperature compensation. If one is made from (or in series with) a material with a positive temperature coefficient and one with a negative temperature coefficient then it is possible to monitor both and compensate, so the throttle position alway corresponds to the same throttle input regardless of temperature... I would have to take one apart and take a very close look to know... but it is one possibility.

Another possible option is if they are reading from opposite ends of the strips. Then they are using the differential voltage between them as the input. This also provides some compensation in itself, since the material properties tend to "drift" in the same manner for like materials. So if the resistance drops for one it drops for the other, the change in the differential voltage is MUCH smaller than the percent change in the resistance values if the correct values are chosen. This works even better if there is a precision resistor of much larger value in series with each. But again, these are just ideas that came up as I read.

There is also some component of the programming of the car that affects the throttle response I believe.. to see this, go out (those who have not tried this mod), and start your car in the cold. Right after starting, punch the throttle a few times and note the response. Now, wait until it is warmed up and do the same, the response is much more delayed after warm up, at least in mine. I have not tried this mod, because I have really never had an issue with the delay (I was used to it very quickly) , but I may try it since it seems to help.

 

Good theories!

The delay that im talking about is when you push/hold the pedal in say a 1/2" and nothing happens at all like the rpms never rise. Not the delay when you punch it to the floor and release right away and then the engine revs a second or two later.

Thats why the mod that i came up with fixes that aspect of the delay whereas a flywheel would fix the other aspect that i mentioned.

 

Good thoughts, but the New Car Features book says the two pots are for redundancy. The ECM checks both of them for agreement before changing the throttle position. It's pretty standard for process controls in critical systems, and the accelerator is definitely a critical system from a legal liability perspective.