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I replaced my old, cracked, nasty TPS tonight with another old, nasty, but functional one. I noticed that the two screws that hold it in are in channels that allow for at least 15 degrees of adjustment in the TPS. The idea seems to be telling the ECU that the throttle is not where it is.

Considering that the throttle is a pretty precise piece of equipment (i.e. very little play at any angle), what would be the point of adjusting the TPS sensor? What would be gained by telling the ECU that the throttle is at 10 degrees open when it's actually fully closed?

I put it back right in the middle of the channel, and the car ran fine, completely normally. You have to take the throttle body off to get to the screws holding the TPS in, so I'm in no hurry to take it back off and mess with it.

Ben

PS: got a good 3mm or so of caked oil off the back of the throttle plate lol.
 

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I had one out of adjustment once and it made the car jerky at very low throttle -- like it went into decel mode while I still had a tiny bit of throttle on. It was a major pain in slow traffic. Adjusting it by a fraction of an inch made a big difference in drivability.
 

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Discussion Starter · #3 ·
Ya, that's what I'm saying. It seems like there's a correct and incorrect place for the TPS to sit, and since the throttle plate doesn't really have any tolerance or play, the correct place is the same place every time -- so why have an adjuster on it?
 

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bentheswift said:
Ya, that's what I'm saying. It seems like there's a correct and incorrect place for the TPS to sit, and since the throttle plate doesn't really have any tolerance or play, the correct place is the same place every time -- so why have an adjuster on it?
Because not every TPS will read the exact same voltage at the exact same angle. The ECU is looking for a voltage to tell it when the car is at "idle" (throttle closed) vs. open (very light throttle), among other things. This is a very small difference in position that creates the voltage difference between the two modes. Plus the manufacturing tolerances of all the components and positions of the holes drilled/tapped into the TB might not be exactly the same on every car. The slots allow for precise adjustment to compensate for all this. There is a procedure for setting the proper position using a feeler gage on the throttle stop so that you get it just right.

I don't think it being off much will hurt fuel/ignition for light/moderate/heavy throttle, as the ECU is mainly looking at the AFM and RPM to determine that, but it can affect (as was mentioned already above) the transition from idle to very light throttle situations easily by being just a tiny bit off.
 

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bentheswift said:
I replaced my old, cracked, nasty TPS tonight with another old, nasty, but functional one. I noticed that the two screws that hold it in are in channels that allow for at least 15 degrees of adjustment in the TPS. The idea seems to be telling the ECU that the throttle is not where it is.

Considering that the throttle is a pretty precise piece of equipment (i.e. very little play at any angle), what would be the point of adjusting the TPS sensor? What would be gained by telling the ECU that the throttle is at 10 degrees open when it's actually fully closed?

I put it back right in the middle of the channel, and the car ran fine, completely normally. You have to take the throttle body off to get to the screws holding the TPS in, so I'm in no hurry to take it back off and mess with it.

Ben

PS: got a good 3mm or so of caked oil off the back of the throttle plate lol.
I was able to adjust the TPS without removing it. It was a matter of getting the old screws out and replacing them with caphead screws and then using a hex key to loosen them up. I don't remember exactly what I did to get the old ones out. But the caphead screws make it a lot easier.

My assumption is that the adjustment is there just to deal with manufacturing tolerances. The TPS contains not just a position sensor (which is probably more looking for change in throttle position rather than absolute throttle position) but also a switch indicating if its in idle (which is essentially a special mode for the ECU). I don't really see any significant advantage to misadjusting it. Like others have said, the main issue is switching in and out of idle mode at the correct time. Despite the fact that mine was correctly adjusted last time I checked, it sometimes seems like my throttle response is poor on very light throttle off a closed throttle plate.
 

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To adjust it correctly, you need 2 feeler guages and a multimeter. IIRC, .015 for the idle position, .026 for the just barely open position, and Theres another test for wide open. If you have a BGB its all in there. A misadjusted TPS will cause an erratic idle- some people have complained about a idle that goes up and down ~500 RPMs. ITA(Norm) turned me on to the solution, if you search for "code 11 CEL" you should get that thread.
 

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sliverstorm said:
there's no switch. There's a diagram in the factory service manual, it's just a few rings of metal with moving arms. Do you know what a potentiometer looks like/how it works? Look those up, that's how this works.
Okay, genius... Yeah, I do know what a potentiometer looks like and how it works, I'm an electrical engineer, I do this for a living, and if you don't believe me that, go look at page FI-58 and FI-59 of the 1985 BGB.

The diagram in the upper left shows that there is a switch between E2 and IDL, as well as a pot with the wiper connected to VTA. Further, on FI-59, step 4(c) says to check the contuinuity between IDL and E2 at .35mm clearance between level and stop screw and then at .59mm. At .35mm there should be continuity, at .59mm there should be no continuity. That sure sounds like SPST switch to me, but maybe you could school me in rudimentary electronics devices.
 

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The TPS should be adjusted so that the switch contacts are closed with a .015" feeler gauge installed between the throttle arm and stop - and open with a .025" inserted. It takes a little fiddling.
 

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It's worth following the BGB setup using the feeler guages. If you don't get continuity between E2 and IDL at idle, when you jumper T and E1 to set your timing, you will be getting a code 11 or 51 (depending on your engine) and no amount of rotation of your distributor will bring you closer than 20? BTDC.
 

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Some background information on the operation of the throttle position sensor:
http://www.autoshop101.com/forms/h33.pdf

Some pictures to help the discussion:

1. The ears on the throttle body match up to the ones on
the throttle position sensor:


2. Throttle body stop:


3. Setting the tps:


4. I removed the plug from a harness to make it
easier to set the tps when it is mounted on the throttle body:


Replacement hex screws from Lowe?s hardware:

I use a small regular or needle nose vice grip plier to loosen the original phillip head screws
 

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Hey all,
Well I am adjusting the TPS per the postings and the Haynes manual for a N/A. My question is does the N/A differ from the S/C TPS settings??? ex. the feller guage and the resistance...

I have a S/C does anyone have the specs. to adjust the TPS???
 

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Same specs, but the S/C TPS is upside down - IOW, the E2 and IDL (which are the only ones you really care about) are on the bottom instead of the top.
 

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Well i think I finally got the TPS set...I used the specs for the N/A and took 2 tries til I got.... Hopefully :goodluck: took it out for a spin and had her running for an hour and no flucuating idle.....

in response to ITA-MR2
not to correct you but the TPS is facing 1 o' clock upwards on the S/C. and I used pin 1&2 all the way to the left as your looking at the TPS....thats how I adjusted the ohms (E2+IDL).....is this correct?
 

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I never meant to imply that the physical orientation was different. The electrical pinouts are different.

Top to bottom - or in clockwise order, IIRC:

N/A - E2, IDL, VTA, VCC
S/C - VCC, VTA, IDL, E2

or . . . upside down.
 

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hpmaxim said:
Okay, genius... Yeah, I do know what a potentiometer looks like and how it works, I'm an electrical engineer, I do this for a living, and if you don't believe me that, go look at page FI-58 and FI-59 of the 1985 BGB.

The diagram in the upper left shows that there is a switch between E2 and IDL, as well as a pot with the wiper connected to VTA. Further, on FI-59, step 4(c) says to check the contuinuity between IDL and E2 at .35mm clearance between level and stop screw and then at .59mm. At .35mm there should be continuity, at .59mm there should be no continuity. That sure sounds like SPST switch to me, but maybe you could school me in rudimentary electronics devices.
nice one
 

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hpmaxim said:
Okay, genius... Yeah, I do know what a potentiometer looks like and how it works, I'm an electrical engineer, I do this for a living, and if you don't believe me that, go look at page FI-58 and FI-59 of the 1985 BGB.

The diagram in the upper left shows that there is a switch between E2 and IDL, as well as a pot with the wiper connected to VTA. Further, on FI-59, step 4(c) says to check the contuinuity between IDL and E2 at .35mm clearance between level and stop screw and then at .59mm. At .35mm there should be continuity, at .59mm there should be no continuity. That sure sounds like SPST switch to me, but maybe you could school me in rudimentary electronics devices.
from the picture in the BGB it looks, at first glance, a whole lot like a simple break in the trace. You don't need a fancy switch when simply moving the arm off one of the traces breaks the circuit. Look at the top pair of contacts (I believe that's IDL and E2) What would happen to conductivity between the two when IDL (the lower of the 2) moves off the printed trace and onto nonconductive material?



an you sure did get offended fast by someone who was just trying to help. Why did you expect me to know what you do for a living? It's not like I'm your stalker or something. And next time before you try to jump down my throat with 'oh well that *sounds* like blah blah blah' at least take a look at the diagrams I tried to point you to.
 

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^^
Actually, in the graphic, IDL and E2 are the bottom pair of contacts. There is continuity at full CCW rotation. The graphic shows it at ~10% throttle.
 

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Figures. Why would it be right-side up, that would make things too easy. Though it still looks to me like there is no *switch*- which really makes a lot of sense to me. The simpler it is, the better; esp. when it will move a bajillion times during it's life. Just think of how many times you've moved your gas pedal.
 
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