All I ever hear, and experience, from the TPS is crap. It's always something the TPS is messing up, I've never heard of any benefits of the TPS, are there any? or did mazda just put it in to screw our cars up?

 

Obviously it was put there to tell the ECU where the throttle plates are. Although the reason our cars mess up so much because if them is because they have 16 year old wiring and sensors. I am sure if you buy a NEW sensor and have a great harness and set it according to the FSM with a Digital Multi Meter you should not have many problems unless you mess with it.

 

No, it's not an infernal plot by Mazda to condemn us to monthly intercooler removal! All EFI cars have throttle position sensors. Being a fairly early design, the Mazda EFI system only uses the TPS to tell the ECU when the throttles are closed. This is so it can switch off the injectors when they're not required to save fuel and prevent bucking under deceleration. S5's also have a second TPS that's full-range and is used to control the electronic OMP. More modern EFI systems use full-range TPS's as another input to more accurately calculate fuel and ignition requirements.
I don't think it's the actual TPS that's the problem (it's just a simple variable resistor), but rather the way it's mounted and adjusted. For some reason it doesn't seem to be able to keep itself in adjustment, but I've never figured out why. I battled this problem for five years on my 12AT-powered '84 Cosmo (exactly the same TPS) and was gutted to find FC's have the same problem.
When you get the TPS adjusted right, the car runs beautifully. Once it's out of adjustmnt you get the annoying bucking caused by the injectors being turned on and off too late in the throttle's travel. Really out of whack TPS's cause wierd idle problems. Don't necessarily rely on the 1V or 1k-ohm settings recommended in the manual. Experiment to find the best setting for your car.

 

Even with my new TPS adjusted to 1v @ Idle, It never seems to stay there, say the next day checking It after a long drive for example.

 

Does that also have anything to do with closed loop or is that done strictly by vacuum pressure?

 

Throttle position has nothing to do with closed loop or vacuum pressure. Three completely different things.

 

i think it might be the old technology, iv had other 80's fuel injected cars and they had TPS proplems too. If we could convert to a new TPS from a new car, that would be great.
Cant you do this with a lot of DFI setups?

 

I know it's different, what I meant was what makes the ECU decide to run in closed loop for the O2 sensor or just full rich? I thought it was the tps, over 100% it went to just dumping fuel, but less then that it went into closed loop for best economy.

 

NZ will probably correct me on this but here I go

I think the ECU on the s4 recognizes 3 (static) setting for the TPS:
- closed throttle (idle time)
- full throttle
- anything in between

now for the dynamic part,

The TPS tells the ECU when you lift your foot from the pedal, so that it can cut fuel as NZ said.

The TPS also tells the ECU when you step (heavily) on the gas so that it can inject more fuel (it's called the accelerator pump effect, referring to a carb setup)

I would think closed loop may only occur when the TPS is steady in between closed and full throttle. Please, NZ, chime in on this if you have more info or more accurate explaination.

At idle, the voltage at the ECU pin for the TPS should be 1.0V give or take. Once you set it, it should always come back to the same position but probably due to temp variations, old age, etc, the plates don't always come back at the very same position, so you might see variations in the voltage but they should be pretty small. If the variations are high, then something is wrong with TPS or the plates linkage.

in any case,
you could always try to run without TPS connected and see how it runs. I have tried once and it was awful. Some pple say their car run fine without it. I saw once on the internet that a disconnected TPS equals full throttle, ECU wise. But can you always believe the internet (anyways, I have the link somewhere).

hugues -

 

SilverRotor......Perhaps it's your thermowax that is giving you different readings? If the tps adjustment screw isn't backing off and the holddown screws for the tps are secure....then just maybe the thermowax is set/rigged a touch off, and the cam and rollpin are touching when the engine is fully hot????? Maybe if you went out there to the car and deliberitly adjusted it where the cam can't possibly toucht the rollpin, and then go for a drive anc check the tps voltage several times, you could determine if that cam/rollpin is causing the different readings.

 

There is a variable resistor inside the TPS plunger.
When it gets dirty, it also can cause inconsistant signals.

 

Nope, the ECU uses the pressure sensor to determine load on the engine.

 

If you have a close look at the TPS when you open the throttle, you'll see the plunger is at full extension after only a very small opening. Basically all it can do is tell the ECU whether the throttle's completely closed or not completely closed. It's a very basic set-up that reflects the system's age.
Even S5's still use a narrow-range TPS for this function, with the second TPS (a full-range one) only controlling the electronic OMP. I think you'll find it's actually the pressure sensor that does this. Because the pressure in the manifold changes much quicker than the AFM's airflow reading, it works perfectly in the "accelerator pump" function.

 

Ah, I see so it's really the pressure sensor that determins this. Makes sense as would be more accurate.