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Thread: Removal of TPS from Throttle Body . . . How?

  1. #1
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    Removal of TPS from Throttle Body . . . How?

    The throttle body is removed from my Euro 320i and sitting on my workbench with both ot the TPS screws removed. Problem: the TPS won't separate from the throttle body no matter in what position I place the throttle shaft -- closed, part-way or wide-open.

    I simply want to remove it to clean it up and to drill the 1/8" - 3/16" oil drain hole which thejlevie recommends; therfore I do not wish to destroy it in the removal process. So please tell me: what am I doing wrong?

    Jeff
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  2. #2
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    Once the screws have been removed the TPS should just come right off the throttle body.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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    With how much force, Jim? I, too, thought that it would come right off once the screws were out . . . but I stopped trying at the point that I thought I would soon break the plastic housing. It is definitely stuck. It will turn radially a short distance to the extremities of the two screw slots, but it will not pull free. Do I dare spray it with Kroil or some other penetrant to hopefully persuade it to let go?

    Jeff
    1984 320i Baur TC2 5-Speed Opalgrün (Jeff's)
    1987 325e Sedan A/T Zinnoberrot (Dawn's)
    1984 633 CSi 5-speed Bronzit (Ours . . . if she says so)


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    Use the Kroil. wait a few minutes , then wiggle it off.
    There is some corrosion that is cementing the sensor body to the Niche in the TB.


    m

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    Okay. Thanks, Jim.

    Judging by the date codes on the components and the "patina" of the untouched fasteners, I think that there are many items on this 320i which have never been replaced or adjusted. The TPS is probably among those.

    It was the same story when I performed essentially the same job on the 325e a year ago. I love the way that these cars last, but I don't love the way that the POs obviously failed to maintain them . . .

    Jeff
    Last edited by BMWtyro; 03-23-2012 at 07:39 AM.
    1984 320i Baur TC2 5-Speed Opalgrün (Jeff's)
    1987 325e Sedan A/T Zinnoberrot (Dawn's)
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    Usually I have to turn the butterfly valve almost to fully open. Just pull the TPS while turning the valve open and it will eventually slip out.
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  7. #7
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    UPDATE:

    Between using Kroil and turning the throttle shaft as gmannino suggested, the TB finally decided to turn the TPS loose. Once removed, it became clear that it was indeed completely filled with oil from the crankcase vapor hose (PCV hose) which runs from the valve cover to the throttle body. I don't know why the thing still worked; maybe it didn't, but the vacuum leaks elsewhere masked that problem.

    Early this afternoon I drilled the 3/16" hole in the exact center of the TPS as Jim suggested, and the switch is still dripping oil tonight. I plan to clean it with spray brake cleaner later this weekend, then test the TPS with a fluke meter to see if it is working properly. Did BMW or anyone else ever come up with an update to keep such quantities of oil vapor from reaching the TB and contaminating the TPS?

    Jeff
    1984 320i Baur TC2 5-Speed Opalgrün (Jeff's)
    1987 325e Sedan A/T Zinnoberrot (Dawn's)
    1984 633 CSi 5-speed Bronzit (Ours . . . if she says so)


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    Quote Originally Posted by BMWtyro View Post
    UPDATE:
    Early this afternoon I drilled the 3/16" hole in the exact center of the TPS as Jim suggested, and the switch is still dripping oil tonight. I plan to clean it with spray brake cleaner later this weekend, then test the TPS with a fluke meter to see if it is working properly. Did BMW or anyone else ever come up with an update to keep such quantities of oil vapor from reaching the TB and contaminating the TPS?

    Jeff
    This would explain why I always have a trickle of oil in the intake boot when I remove my air box. Would also like a "solution" and if there's a how to link on drilling that hole, I'd appreciate it.
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    If you are looking for a fix, your best bet is an after-market oil/air separator installed on the vent line. You can check a site like summitracing.com for them.
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    Quote Originally Posted by richardodn View Post
    If you are looking for a fix, your best bet is an after-market oil/air separator installed on the vent line. You can check a site like summitracing.com for them.
    Thats funny. I just sold one for an M54 since I had no use for it. Seems this is a common conditions on M20's. Does not having one cause issues or is it more just a nuisance ?
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  11. #11
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    Oil in the intake is normal and there can be quite a bit on an engine with more than 100k. While not particularly good, oil going through the intake isn't harmful unless the volume is enough to cause fouling of the plugs. Placing a catch tank that incorporates an oil separator between the valve cover and intake will greatly reduce how much oil reaches the intake.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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    Quote Originally Posted by thejlevie View Post
    Oil in the intake is normal and there can be quite a bit on an engine with more than 100k. While not particularly good, oil going through the intake isn't harmful unless the volume is enough to cause fouling of the plugs. Placing a catch tank that incorporates an oil separator between the valve cover and intake will greatly reduce how much oil reaches the intake.
    Good to know its not a concern as long as your plugs are clean and I suppose if they aren't, best it be through the intake rather than blow by.
    Last edited by Jeffnhiscars; 03-24-2012 at 12:13 PM.
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  13. #13
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    Jeff,

    Jim Levie taught me the trick of drilling that hole in the bottom of the TPS; I don't know if there is a link pertaining to it.

    You drill a 1/8" to 3/16" hole with a normal steel drill bit in the exact center of the circular depression, with the drill tip entering precisely at the bottom of the "S" in the word "BOSCH" which is embossed into the bottom of the switch. This should put you on dead-center with the switch's central bore into which the throttle shaft extends. The plastic isn't very thick, so be careful. Drill a smaller pilot hole first if you wish, just to be certain that you are on-center.

    I suppose that you could also drill down through the bore from the top of the switch as well, but I would use only the 1/8" bit if I chose to do it that way since you stand a chance of wiping out the plastic "flat" which engages the "D" on the throttle shaft end if you use a bigger bit.

    Jeff
    1984 320i Baur TC2 5-Speed Opalgrün (Jeff's)
    1987 325e Sedan A/T Zinnoberrot (Dawn's)
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    Im not that familiar with the M20 TPS but am having trouble visualizing the point of drilling the hole, especially on top. It seems like you're creating an intake leak but that's way too obvious to be the case.

    I know Im missing something here

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    Quote Originally Posted by Jeffnhiscars View Post
    Im not that familiar with the M20 TPS but am having trouble visualizing the point of drilling the hole, especially on top. It seems like you're creating an intake leak but that's way too obvious to be the case.

    I know Im missing something here
    Once you pull your TPS off take a look at how the tbody shaft inserts into the TPS. Also look at how the shaft exits the tbody. That should make it easy to see where to drill the hole on the TPS and why the hole won't present a vac leak.

    It seems tricky and hard to understand only because you've not done it yet.

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    Quote Originally Posted by RangerGress View Post
    It seems tricky and hard to understand only because you've not done it yet.
    Of course... 100%...Im not fazed by the concept, but I wouldn't do it just to understand it since I don't even see the point of it..lol
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  17. #17
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    Jeff,

    Being a bit more familiar with fuel systems in general than most (though admittedly not very familiar with this fuel injection system), there is in theory no vacuum escaping between the lower throttle shaft and its bearing surface. I say "in theory" because as close-tolerance surfaces wear, a bit of vacuum will inevitably seep past those surfaces; that is why I am forever re-bushing/re-sealing the carburetor throttle bodies which my customers send to me.

    Had I found "slop" in my throttle body's shaft, I probably would have re-bushed or re-sealed it if the design lends itself to that repair (I didn't bother to investigate that possibility since it was nice and tight).

    The hole itself is not intimidating to drill. First, confirm that you can indeed place a 1/8" (or larger) bit from the top of the switch down through the hole in the center to the bottom without interfering with anything inside the switch. I chose to drill into the switch's case from below (outside) to avoid plastic shavings being left inside the switch body, and if you take careful measurements to determine the exact center of the "bulge" on the switch's bottom, you can do it as well. On mine, I put the drill point against the very bottom of the "S" in "Bosch", and it went through without hitting anything.

    Jeff
    Last edited by BMWtyro; 03-25-2012 at 09:20 AM.
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    Quote Originally Posted by BMWtyro View Post
    Jeff,

    Being a bit more familiar with fuel systems in general than most (though admittedly not very familiar with this fuel injection system), there is in theory no vacuum escaping between the lower throttle shaft and its bearing surface. I say "in theory" because as close-tolerance surfaces wear, a bit of vacuum will inevitably seep past those surfaces; that is why I am forever re-bushing/re-sealing the carburetor throttle bodies which my customers send to me.

    Had I found "slop" in my throttle body's shaft, I probably would have re-bushed or re-sealed it if the design lends itself to that repair (I didn't bother to investigate that possibility since it was nice and tight).

    The hole itself is not intimidating to drill. First, confirm that you can indeed place a 1/8" (or larger) bit from the top of the switch down through the hole in the center to the bottom without interfering with anything inside the switch. I chose to drill into the switch's case from below (outside) to avoid plastic shavings being left inside the switch body, and if you take careful measurements to determine the exact center of the "bulge" on the switch's bottom, you can do it as well. On mine, I put the drill point against the very bottom of the "S" in "Bosch", and it went through without hitting anything.

    Jeff
    I grasp the "how to" part as well as I can without actually doing it. I'm not hearing the "why bother"...what does this accomplish ?
    Last edited by Jeffnhiscars; 03-25-2012 at 11:17 AM.
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  19. #19
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    Jeff,

    Aww, shoot -- I didn't realize that the "why" had not been discussed here on this thread.

    As hot oil vapor is drawn into the throttle body through the PCV system, some of it invariably wicks its way down past the throttle shaft and into the TPS below it. I imagine that this happens mostly after shut-down. It is a gradual process because, as stated earlier, that shaft is fairly tight unless its bearing surface is worn.

    Eventually, the switch will become so fouled with oil that it ceases to make the correct contact when the throttle position returns to idle. The engine will then surge, much as if it has a vacuum leak. You will chase your tail looking for vacuum leaks until someone finally says "Hey, by any chance is your TPS full of oil?" . . . whereupon you learn about this trick which Jim taught to me.

    Jeff
    1984 320i Baur TC2 5-Speed Opalgrün (Jeff's)
    1987 325e Sedan A/T Zinnoberrot (Dawn's)
    1984 633 CSi 5-speed Bronzit (Ours . . . if she says so)


  20. #20
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    Quote Originally Posted by BMWtyro View Post
    Jeff,

    Aww, shoot -- I didn't realize that the "why" had not been discussed here on this thread.

    As hot oil vapor is drawn into the throttle body through the PCV system, some of it invariably wicks its way down past the throttle shaft and into the TPS below it. I imagine that this happens mostly after shut-down. It is a gradual process because, as stated earlier, that shaft is fairly tight unless its bearing surface is worn.

    Eventually, the switch will become so fouled with oil that it ceases to make the correct contact when the throttle position returns to idle. The engine will then surge, much as if it has a vacuum leak. You will chase your tail looking for vacuum leaks until someone finally says "Hey, by any chance is your TPS full of oil?" . . . whereupon you learn about this trick which Jim taught to me.

    Jeff
    Well, I'm glad we figured THAT out..lol

    I thought we were discussing minimizing the risk of plug fouling and all of a sudden we are drilling holes in the TPS. I did not think my Saturday night was that rough
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