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Thread: Can anyone explain the e30 tps mechanism?

  1. #1
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    Can anyone explain the e30 tps mechanism?

    My car has been having symptoms of a faulty throttle position sensor with bucking, hard shifts, idle problems etc. I unplugged the tps today and didn't notice any difference in the way the car performs.

    So I took it off and took it apart but didn't seee anything wrong inside other that it was drenched in oil. There is a little white box with a clicky thing that I think is pushed when the throttle is all the way closed, I assume for idle...Also 2 little prongs that push together when the throttle is all the way open...But there seems to be no active mechanism that would detect throttle position for regular throttle.

    Does anyone know how they work for certain?

    here is a picture. note the oil drenching

    Last edited by otto325e; 07-20-2011 at 07:00 PM.

  2. #2
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    Well the throttle position sensor is really only used for WOT and Idle. Between those two it doesnt send a signal to the computer.
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  3. #3
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    ohhh...how common is it for the idle sensor to quit? Would it being drench with oil ruin it?

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    Not necessarily ruin it, but it could prevent the contacts from closing. Cleaning it out would take care of that.

    The only E30 with a throttle position sensor (as opposed to switch) is the M42.
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    the throttle position switch signals the computer when throttle is closed and then again for wide open. the computer trims the fuel accordingly.

    Quote Originally Posted by richardodn View Post

    The only E30 with a throttle position sensor (as opposed to switch) is the M42.
    not so much of a sensor, but a potentiometer.
    Last edited by Tom D; 07-20-2011 at 08:17 PM. Reason: Automerged Doublepost
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  6. #6
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    the thing that caught my eye was "drenched in oil". sounds like you have a lot of oil blowby, due to bad rings.
    how are the plugs, wires, cap and rotor? not to mention compression/leak down?

    check the TPS with a multimeter. make sure the 2 contacts have continuity when closed, then make sure it is adjust properly at idle. off idle it really has no function other than to say it is not at idle.

    make sure you dont have any air leaks too.
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    Quote Originally Posted by Tom D View Post
    not so much of a sensor, but a potentiometer.
    That's how many automotive sensors work. Variable resistance due to position (AFM, fuel level) or temperature (temp gauge sender)
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  8. #8
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    Sorry to correct you guys but the TPS is not a potentiometer nor does it provide any voltage or current dividing.

    The TPS is comprised of two normally open contacts, one of which closes during idle and the other during wide open throttle. As you can see in the picture, its nothing more than a pair of contacts and another pair inside the micro switch.

    Its simply a switch toggled by throttle position. It is also normal to see oil inside of the unit, every TPS I've ever removed and opened had some oil. The oil comes from oil vapor which feeds from the valve cover breather hose into the throttle body itself.

    Its best to test the adjustment with a DMM but it can be tested by listening. Near idle, by moving the throttle cable arm, you should hear the "click" of the micro switch. At near 70% full throttle, per Bentley manual, you should hear another click. If you're hearing only 1 click, its out of adjustment range and needs to be readjusted.
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    Quote Originally Posted by gmannino View Post

    ……..Sorry to correct you guys but the TPS is not a potentiometer nor does it provide any voltage or current dividing.

    The TPS is comprised of two normally open contacts,
    that's exactly what richard and i both said. the potentiometer or sensor if you will, only came on the M42 powered E30. the M20 E30 had a switch.
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    Yup, just noticed that. Sorry lol
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  11. #11
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    Yep it was definitely not adjusted properly. There is a click now that wasnt there before.

    Now that I think about it, I remember taking it off last november and not knowing how to reinstall it or whether it mattered which way it was turned then fastened. The car seems to not buck and go insane at low rpm with the clucth out now.

  12. #12
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    how to adjust TPS?

    Quote Originally Posted by gmannino View Post
    Its best to test the adjustment with a DMM but it can be tested by listening. Near idle, by moving the throttle cable arm, you should hear the "click" of the micro switch. At near 70% full throttle, per Bentley manual, you should hear another click. If you're hearing only 1 click, its out of adjustment range and needs to be readjusted.
    How does one go about "adjusting" the TPS? I have a high idle issue on an S14 motor (idles @ 1200 RPM) and rumor has it the usual suspect is a bad or maladjusted TPS. It is not the exact same part number as on the M20 motor but looks very similar and is easier to access.

    Any feedback appreciated...

  13. #13
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    I don't know any of the particulars of adjusting it on the S14. Have you looked over at http://www.s14.net/forums/ ?
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  14. #14
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    I don't have any docs on this but if the TPS on an S14 is similar and has just idle & WOT switches, it probably would be adjusted the same as other E30's. That means adjusting the TPS so that the idle switch closes when the throttle stop arm is 0.030-0.060" off the idle stop screw.

    You can necessarily go by the click. The idle switch can click and yet not make an electrical connection. Use an ohmmeter to verify operation of both the idle and WOT switches. When adjusting the TPS is is best to use a meter or test light.
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    ....and make sure the computer sees the signal. With an open you can adjust all your life and never get it from point a to point b. (If adjusting does nothing)
    I like to test stuff before I replace it, it makes me feel better about expensive parts.

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  16. #16
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    re: s14...the tps is mounted with two screws. when they are loosened you can rotate the tps on the throttle shaft slightly to adjust it at idle.

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    Reviving an ancient thread...

    Thanks very much for the photo of the inside of the switch. My switch is adjusted correctly but the WOT function is intermittent which is to say it sometimes "beeps" the multimeter and sometimes the resistance lingers around ~25-75 ohms. This to me sounds like oil on the contacts. I see the little plastic tabs around the perimeter of the switch... did you just use a pick to open this puppy up?

    One wrinkle - Bentlely specifies the WOT test by "slowly opening the throttle". When I do this by hand, in a relaxed manner I get continuity pretty much 100% of the time. When I simulate "flooring it" or the stomp test I get decidedly mixed results. Does anyone know if ~25-75 ohms would lead to enough voltage to trigger the full throttle signal to Motronic?

  18. #18
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    No e30s, again :(
    you can use whatever to undo the little latches. pick, small screwdriver, knife tip, whatever.

    as far as the rest of your question, no idea
    No e30s again.

  19. #19
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    Quote Originally Posted by somecarguy View Post
    Reviving an ancient thread...

    Thanks very much for the photo of the inside of the switch. My switch is adjusted correctly but the WOT function is intermittent which is to say it sometimes "beeps" the multimeter and sometimes the resistance lingers around ~25-75 ohms. This to me sounds like oil on the contacts. I see the little plastic tabs around the perimeter of the switch... did you just use a pick to open this puppy up?

    One wrinkle - Bentlely specifies the WOT test by "slowly opening the throttle". When I do this by hand, in a relaxed manner I get continuity pretty much 100% of the time. When I simulate "flooring it" or the stomp test I get decidedly mixed results. Does anyone know if ~25-75 ohms would lead to enough voltage to trigger the full throttle signal to Motronic?
    Are you having any issues when driving and actually going WOT on the pedal? or is it not running yet?

  20. #20
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    It was running "fine" before the teardown, but there are several threads on dyno results of cars where the ECU doesn't receive the WOT signal, doesn't go into closed loop mode and therefore runs at the wrong AFR at WOT. I'm not necessarily chasing extra ponies I just want the car to run (and self-diagnose) as it was intended.

  21. #21
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    How did you guys even get this thing open? I'm scarred the plastic is about to break if I use too much force.

    Are those 4 plastic prongs on the top half actual clips that need to be pried outwards away from the bottom half?

  22. #22
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    Most of the time you really don't have to open it up. Just drill a couple of small holes on the bottom (when mounted) to allow any oil to drain out. Use some cleaner (electrical contact cleaner, brake cleaner, carb cleaner, etc.) sprayed into one of the holes and flushed out the other. Make sure you don't end up accidentally spraying it in your eyes. That's usually enough to get it functional.
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  23. #23
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    Some people just dont want to drill holes into these expensive little parts

    I got mine open with difficulty. They are glued closed, so first time will be a biatch. Trying to knock the bottom half off was very awkward because the only spots you can grab it (or clamp it with a vice) presses the edges of that half onto the very other half you are trying to knock out.

  24. #24
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    drill a small hole carefully it will stop it happening again and cause no issues
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