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    TPS test and install

    Need some views and opinions on this. While testing and looking for why my idle has a little miss and my mpg is down a little, it came time to test the TPS. First my idle is steady and only sometimes, does it stay at a higher rev, like 1200 for a few seconds about once every 3 weeks. So I have few questions on it. The unit has 3 pins, top, middle and bottom. In the e30 m42 factory repair manual they have pin numbers, 2, 18, and 3. Very hard to see on my current TPS which pins they are but with the way the TPS works and reading lots for stuff online, no need to know which ones they are specifically. One pin is for WOT and idle. As per factory manual, you need to test the leads between the middle pin and the any of the other two and you should get 0 ohms. With the WOT pin, you need to open the throttle manually all the way.
    From reading the e36 Bentley, it seems to change the pins on the TPS, which is the only one to cover the m42, it labels the pins, 1,2 and 3 in sequential order. It states to make sure the TPS is get 5V by testing the connector at pin 1 and a ground. Here is the confusing part as it says to test pins 1 and 2 and pins 1 and 3 to see the ohm reading but contrary to the factory manual,
    it states you should have about 4k ohms. With one of the pins sets, the values will go up until it gets to 4k.

    It looks like it is two different tests with the same device. I will run these to see what I get but was wondering what other have seen or done to test the TPS. Maybe one of them is wrong. Also these factory manuals state that the TPS is adjustable but turning it which the mounting screw is loose in the slot while the Bentley states it is not. Reading online, the consensus seems to say it is not adjustable.

    I do believe my issue is something with a leaky injector or maybe O2 sensor, as when I turn the car on, cold or warm, I get a big fuel burn smell from exhaust. I have tripled check for vac leak at hoses, tested AFM and have no fuel leak. This all started to happen after my last rebuild so maybe I kinked an injector while installed on the intake manifold. They were overhauled about 5
    years ago. I did test my O2 then after this recent rebuild and it tested within spec.

    Thanks for any insight on this issue.
    Alex 88 m5 | 91 318is | 19 Subaru Ascent
    BMW Tool Rentals & Fender Roller

    #2
    I finally had a chance to test today and using both sets of instructions I had different numbers. Only thing for sure is that the TPS is getting 5V. Using the e36 manual I get 4.6k ohms at idle which it suppose to be 4K and when at WOT, I never get anything near 0 ohms like it should be. I will get a used on from the junkyard first and many different models until 1999 used them. I will will verify its numbers before I order a new one. Don't want to spend over $50 on something I don't need. Hope this is the my culprit.
    Alex 88 m5 | 91 318is | 19 Subaru Ascent
    BMW Tool Rentals & Fender Roller

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      #3
      Thank you for starting this, I have garage queen that unfortunately i don't get to start and warm her up or drive around that often or regularly as I should...but anyway Started it yesterday and idle is rough I thought it was just a carbon build up issue so i took her out around town high revs but still no luck. It can be several things but my thoughts are start with tps or 02 sensor since i have not replaced both yet...Ill also check my plugs... I know my wires are good... I hope you find the Culprit too...Thanks again...Ray
      1991 325i coupe
      1992 318i conv
      2002 540i sedan
      sigpic

      What did the e30 owner say to the other e30 owner? LOOKING GOOD!

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        #4
        Today I went to the junkyard and had my list of BMW from the 90s that use the same TPS. I found the youngest BMW and took it, a 95 e36. I used the e36 Bentley test as Colin stated above. I get 4.5k ohms between ping 1 and 3. Using a flat screwdriver, I can rotate the TPS as it stops in each direction. Using pins 1 and 2, which on our cars, pin 1 is on top, on e36, it is on the bottom, I get .86 ohms and as it rotate it towards WOT, it climbs up until its max of 5.3. Another thing I find interested is why some documentation states that the TPS is adjustable, is when you look at the TPS on the car which is probably original on my car from 91, the plastic housing for the mounting screws are slotted. So it looks to be adjustable. But on the 95, the holes or just circles which means you set it and forget it. When I tested my current TPS on the car, the reading between pings 1 and 3 are the same but for pins 1 and 2 are opposite. The number is almost 5k ohms and as I move the throttle to WOT, it drops in value until about 2k. So it looks my TPS is shot. I will now order a new throttle housing gasket as you need to remove it to remove/install the TPS. Also this gasket is old as I did not replace it when I did the mess under the intake clean up. I will report after I swap the TPS out.
        Alex 88 m5 | 91 318is | 19 Subaru Ascent
        BMW Tool Rentals & Fender Roller

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