Throttle Body Potentiometers

[Turboman]

Hi !

 

I have a Skoda Felicia 1998, with the AEE engine (1,6 litre, Magneti Marelli injection).

 

The engine doesn´t idle very well, and sometimes stalls completely, and the throttle response isn´t that good either, so I checked over the engine, changed sparkplugs, rotor and cap, they where all quite worn, and things got a little better, but not perfect, so I checked for trouble codes, and there is a code 00516, which is "throttle position switch closed".

 

Did some measuring and the idle motor seems to work ok (V60), and the switch (F60) is closed with engine off, and opens when engine is started, so that seems ok to me, idle motor measures about 6 Ohms between pin 1 and 2 on the TB, and the switch has 0 Ohms between pin 3 and 7, and then changes to infinite when engine is started.

 

Measured the potentiometers in the throttle body too, and the one that is telling the ECU how to run the idle motor (G88) has some (at least in my eyes) strange values, with the throttle untouched it has 690 Ohms, and with the throttle wide open 720 Ohms, measured between pin 4 and 8 on the TB, that is on a potentiometer that seems to have a total range of 1800 Ohms at least (got the total value by measuring between pin 4 and 8, and 7 and 8, and adding those values to each other).

 

The potentiometer that tells the ECU the throttle position (G69) has a value of 670 Ohms with throttle untouched and 1300 Ohms with the throttle wide open, measured between pin 4 and 5 on the TB, that on a potentiometer that seems to have a total value of 2000 Ohms.

 

The throttle body is the one with an 8 pin contact where the pins are in two rows, part number 030133064D

 

If someone has the values that  these potentiometers should have when they are ok I would be very happy if that person could share them

 

Best regards and thanks in advance

 

Mats

[dohnjoe]

the TPS potentiometer gets worn out around idle position.

when faulty will cause rough running, lack of power and idle speed problems.

you can't do very much, other than replacing the TB.

as for measuring TPS integrity, here is how a sweep test is done properly.

[TeflonTom]

I seem to remember that the idle position and throttle pot are wired in series so the value the ecu sees for measuring load is a sum of the both, but the idle position is centre tapped, there was always something odd about the resistances measured on the throttle body, they never make sense.

[dohnjoe]

there are 2 potentiometers connected in parallel.

 

[Turboman]

I seem to remember that the idle position and throttle pot are wired in series so the value the ecu sees for measuring load is a sum of the both, but the idle position is centre tapped, there was always something odd about the resistances measured on the throttle body, they never make sense.

The potentiometers are not in series, at least not according to the wiring diagrams, both are supplied via pin 4, and the other end of the potentiometers are connected to ground via pin 7, the output for the throttle position sensor (G69) is on pin 5 and the pot for idle control (G88) is on pin 8.

 

I´ll do a sweep test as dohnjoe suggest, that should tell me a little more about whats going on.

 

/Mats

[Turboman]

the TPS potentiometer gets worn out around idle position.

when faulty will cause rough running, lack of power and idle speed problems.

you can't do very much, other than replacing the TB.

as for measuring TPS integrity, here is how a sweep test is done properly.

Have done a sweep test now, with a analogue multimeter, and the potentiometer for throttle position seems ok, varies between 4 V at no accelerator and 1,2 V at full throttle, the pot for idle control, is at a steady 1,2 V regardless of throttle position, so that seems to be the problem. Will swap the TB and see what happens.

 

/Mats

[Turboman]

Got the original TB to day (it was swapped about a month ago), so I took the cover off it, and got an answer to why the idle control pot didn´t give any variation in resistance or signal, the G88 pot (idle speed regulation) isn´t controlled by the throttle cable, it´s controlled by the idle control motor!, the throttle cable works only on the G69 pot (throttle position) and the F60 idle switch. Measured with the cover off and turning the idle control mechanism by hand, the G88 pot also seems to produce normal values.

 

And as I come to think of it, the fault code 00516, closed idle switch, is bound to be set as the switch has closed as it´s normal position when the engine is at idle, so that code doesn´t really tell anything, as long as it isn´t linked to the G69 pot value too (like an "and" function, "closed F60" AND "G69 indicating throttle" equals a set fault code), but I don´t know if the ECU is that intelligent.

So it seems that I have two TB:s that produce the same values, so the TB is probably not at fault.

 

I really don´t know what could be wrong now, maybe the ECU ?, but that would produce a bunch of fault codes I imagine, anyone who has an idea is very welcome to share it.

 

Anyone that knows how to attach an image to a post by the way?, I took some photos of the inside of the TB if someone is interested in seeing them.

 

/Mats

[dohnjoe]

my bet would be on a vacuum leak

[Turboman]

Thanks to dohnjoe I got a tip about how to fix the images without having to downsize them, here is the links:

 

 

This is the F60 switch

 

 

This is the inside of the TB, to the lower right is the V60 idle motor

 

 

The outside of the TB

 

 

To the left is the Idle control pot (G88) and to the right is the Throttle position pot (G69)

 

/Mats

Edited 4 August, 2014 by Turboman

[Turboman]

Have searched for vacuum leaks today, didn't find any, sprayed ether all around the engine, not even the tiniest indication of a leak anywhere.

 

Took out the TB that was in the car, took it apart, looked as good as new inside, same measurements on the Idle control pot (G88) as with the other TB, did a little clean up around the damper, maybe just maybe I can notice a little improvement in idling, I'm not sure.

 

Will leave it as it is for now and drive the car and see how it behaves.

 

Thanks for all the input !

 

/Mats

[dohnjoe]

never heard of ether being used as vacuum leaks detector.

I used propane with success.

just to see how engine reacts when ether is sucked in small quantities (like through a small crack), try this:

expose TB entrance and spray small quantities of ether inside.

if idle changes, ether is good for testing.