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I have an automotive electrical issue I am having trouble with, the injection ECU is reacting to the throttle position sensor too quickly and shutting the fuel off on a trailing throttle too early making the reaction to closed throttle jerky, there was a manufacturer recall on my vehicle in 1992 that was never performed and now the dealer and manufacturer knows nothing about it obviously. I found the information supplied to the dealers detailing the fault and remedy but information is sparse as is my electrical knowledge, the fix involves the fitting of a capacitor between the tps ground and voltage signal wire to the ecu from the throttle position sensor which is just a variable resistor that is supplied 5vDC and varies the voltage back to the ECU between .5v and 4.5v depending on the throttle position, my problem is what capacitor should i use? no details are given in the document. I think the idea behind the fix is that when you close the throttle the signal voltage drops from the TPS to .5v but the remaining charge in the capacitor allows the voltage on this signal line to bleed away a second or so slower as seen by the ECU but i do not have a great enough understanding of electrical components to be able to even start choosing the right capacitor. Any help appreciated.

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  • I think we'd need to see all the information you have available. Did they provide any diagrams, values, or written text? It would be better to include everything you have available. The information may be sparse. But it is sparser still to us, if you don't carefully document what you have on hand.
    – jonk
    Sep 25, 2017 at 22:56
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    I think the throttle position circuit would be considered a safety-critical item, and would not consider modifying it in any way other than by using the manufacturer-approved parts. If you've used the car since 1992, you should be able to continue using the car without this modification.
    – Peter Bennett
    Sep 26, 2017 at 0:09
  • I agree with @PeterBennett. The part is still available (~24€) and OEM-approved. So why improvise on a safety critical component?
    – Martin
    Sep 26, 2017 at 7:29
  • I have just rebuilt a V6 engine and fitted it in place of a 4cyl, i think because the modification was applied to the loom and later the ECU revised i have missed the mod as i built the loom myself and have an early ECU type, the TPS is not safety related, it is just used, in part to calculate airflow and fueling, with the auto gearbox equipped cars (mine) it is also used to initiate the fuel cut off on a trailing throttle and activate the idle control valve,, the car will drive with the TPS unplugged but power is reduced and idle control is disabled.
    – Deanxm1
    Sep 26, 2017 at 8:34
  • Tried two other dealers, part is NFP - (no further parts) and they have no information on the specifications either
    – Deanxm1
    Sep 26, 2017 at 8:44

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Being a safety issue the throttle potentiometer would most likely be low in impedance for better immunity from EMI ( ~1k ) and with a desired lag response on the order of 100 ms or so, I would expect C to be an electrolytic and thus I would obtain values ~ 100 uF. Make sure you apply -ve terminal across the throttle to ground with the correct voltage polarity.,

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  • The best option so far - in the light of sparse information and a sensible value of capacitor.
    – Solar Mike
    Sep 26, 2017 at 4:26

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