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Throttle switch click 200

posted by  dnordin on  Tue Aug 31 13:16 CST 2021
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Car is a 91 240 sedan auto.
I have had some drivability issue, mainly stalling just when coming off of idle. So when I checked the throttle position switch when the throttle body was on the car I could not hear a click when opening the throttle. When I removed the throttle body assembly and I move the throttle lever I can hear a faint click. but I have to have my ear to the switch to hear it. Is that normal or should be a noticeable click like a relay or louder?
--
1991 240 Sedan auto








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    Throttle switch click 200

    posted by  Dave Stevens on  Tue Aug 31 14:12 CST 2021
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    last visit: Sun Jan 1 02:36 CST 2012
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    It is indeed a faint click that you may not readily hear on the car. The simplest way to test whether a TPS is malfunctioing and that the switch is being seen by the ECU is to use Diagnostic Test Mode 2 (DTM 2) on port 2 of the OBD connector. See the FAQ here on how to do that. The fourth bullet point is the test for the TPS.

    Being that you heard it click when the throttle body was removed, but not on the car, do be sure that adjustment of the throttle cable and the linkage rod turnbuckle between the spindle and throttle are not preventing the throttle from fully returning to the closed position.

    As for your driveabilty issue of stalling coming away from idle, check the adjustment as well as the operation of the TPS and as well be suspicous of a sticky/worn/dirty IAC valve. If the throttle plate stop screw has been played with in an attempt to change idle, it can create all kinds of such problems. Less likely to be your problem, but still important to check, be sure that all air induction and PCV hoses are fully seated, there are no splits and the clamps are snug, Especially check the underside of the main air intake tube for splits in the accordion section. When coming away from idle, the engine will twist on its mounts and could open up a split there.
    --
    Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now








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      Throttle switch click 200

      posted by  dnordin on  Tue Aug 31 15:13 CST 2021
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      Thanks for the advise. After cleaning everything I can hear the click a bit better. But I am going to go back through everything from the beginning and make sure its set correctly. The only code I was getting is 2-1-4, which I think is an intermittent signal from the crank position sensor?

      --
      1991 240 Sedan auto








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        Throttle switch click 200

        posted by  Dave Stevens on  Tue Aug 31 20:53 CST 2021
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        last visit: Sun Jan 1 02:36 CST 2012
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        If you're getting the 2-1-4 code then the CPS (crank position sensor a.k.a. RPM sensor, mounted in the top of the trans bell housing) is quite more likely to be behind your occasional stall problems than the TPS based on the symptoms you described. As I suggested, the engine twists as you move away from idle and any slight movement could easily cause an intermittent electrical connection or ground sheathing for the signal to misbehave.
        o Inspect the CPS cable carefully, especially down near the base and where it's close to the metal tubing. Any evidence of damaged/worn insulation is cause to replace it. Some people will attempt to repair the damage with mixed results, but they're not that expensive so just replace it, even with an aftermarket brand from a respected supplier if you're on a tight budget.
        o Start by clearing the diagnostic codes, both in socket #2 and in socket #6 (see the FAQ). If the 2-1-4 code returns, a faulty CPS is more than likely the culprit. There are other missing signal possibilities if the wiring has been disturbed to the ECU, but the CPS is by far the most likely cause behind that diagnostic code.
        --
        Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now








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          Throttle switch click 200

          posted by  dnordin on  Wed Sep 1 12:42 CST 2021
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          Thanks Again Dave,
          I have replaced the CPS twice in the past 2 years, the wiring from the sensor to the Connector is new, the rest of the wiring looked OK based on a visual inspection. I do have either a transmission pump leak or a rear main seal leak as I can see oil leaking from the bell housing. I had the transmission resealed by a volvo shop when I bought the car a few years ago, but they did not want to replace one of the seals as they said it could end up requiring disassembly of the trans to get to that one. Funny thing is that the level in trans or the engine does not really change much over time. Although a small leak can make a mess when it is flung around in the bell housing.
          Do you think that that oil is fouling the sensor? I did not think so as the sensor appears to just be a magnet that sends a signal to the computer based on the flywheel teeth, or a reluctor passing by it and interrupting the magnet field. One sensor was a bougicord, the other was Italian but I forget the name. Maybe some dielectric grease on the face of the sensor would help when I replace it???
          The CPS sends a signal to the ignition amplifier, if I am not mistaken, could that be a culprit?


          Thanks,

          Don
          --
          1991 240 Sedan auto








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            Throttle switch click 200

            posted by  Dave Stevens on  Wed Sep 1 16:20 CST 2021
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            last visit: Sun Jan 1 02:36 CST 2012
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            Had to replace the CPS twice in the past two years? That’s not particularly normal. Could it be gone again for the same reason?

            The CPS signal goes to the EZ ignition control module then to the fuel ECU. Even though the 2-1-4 code is set by the ECU (read on OBD port 2) and suggests a wiring fault between the ignition module and ECU, unless you’ve been touching that wiring or had other problems under the dash then more often than not it's still a problem with the CPS providing an intermittent or weak signal. The CPS cable is like coax with the ground as a foil shield to protect from signal loss or interference. That shield needs to make a good ground at both ends and be undamaged throughout it’s length to provide full shielding. An intermittent or weak signal could be a failed or possibly fouled sensor head, damaged wire in the cable (where you may or may not be able to see visible external damage), or a bad contact at the connector. I have not heard of fouling at the sensor tip, but I suppose it's possible.

            Originally, there are one or two plastic standoff clips for the cable attached to the piping behind the block so there is no scuffing on the piping AND so that flexing from engine movement happens over a wide segment of wire between the firewall and the top clip. If the clips are missing then more flexing will happen down by the sensor head on the bellhousing which leads to premature failure of the wire there. I imagine one of the main differences between a Volvo CPS and a cheap aftermarket one is the quality of the wire in the cable. The standoffs often break or go missing after a few years. You can fashion your own standoffs using fat zip ties (black UV type will last longer) and a short bit of nylon/rubber hose/tube.
            --
            Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now







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