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Intermittent Miss at Idle. 700 1987

posted by  pbrown on  Tue Mar 18 05:42 CST 2003
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I have done everything looking for a vacuum leak. I have listened, I have sprayed hoses and injectors with carb cleaner and have even used the unlit propane torch. Nothing helps the miss go away so I'm leaning away from the leak theory. I'm pretty sure it isn't spark related because the miss only happens at idle and then only intermittently. I guess my question is, would a dirty clogged injector cause this? Or could it be the O2 sensor. (It's about the only component I haven't replaced.) Otherwise it runs like a top.

'87 760 B230FT








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    Intermittent Miss at Idle. 700 1987

    posted by  DaJet on  Tue Mar 18 06:46 CST 2003
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    last visit: Tue Jul 3 10:50 CST 2007
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    I am having the exactly the same problem as you are with my 87 740T. I too have eliminated the possibility of a vacuum leak. I have run injector cleaner through the tank many times with no improvement. I even pulled the injectors and the rail off and checked the spray pattern and it looked good. The compression is an even 145-150 across all 4 cylinders.

    I 'borrowed' the distributor, coil. ignition wires and IAC from my friends 740T that idles as smooth as silk, but no change... My idle seems to miss more when the engine is warm or when the car sits at idle for a longer time.

    The funny thing is that my car accelerates better than my friends 740T. And just as you said, my car has no miss or performance problems at highway speed...

    I have replaced the normal tune items, such as plugs, cap, rotor, wires, air filter. I have cleaned the TB, IAC, PCV, and I replaced the intake & exhaust manifold gaskets. In addition I have replaced the engine wiring harness and ECU.

    All of the above in the last 6 months or so...

    I too am thinking that perhaps my O2 sensor may be defective. Or perhaps the Ignition computer?

    I would really like to solve this nagging problem...

    JJ
    87 745T - 255K miles

    JJ







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      Intermittent Miss at Idle. 700 1987

      posted by  DaJet on  Tue Mar 18 18:02 CST 2003
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      last visit: Tue Jul 3 10:50 CST 2007
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      A little update on this issue...

      I checked my O2 sensor signal this afternoon and mine bounces wildly between about 0.13v and 0.78v. changing about 1-2 times per second. Just for comparison, I also tested the O2 sensor on my buddys smooth-idling 740T and his O2 sensor sits nice and steady at about 0.7v

      I did try to run my car on idle with the O2 sensor disconnected but it did not help... I was thinking that if my wildly jumping O2 output voltage is causing the ECU to vary the mixture like crazy, then un-plugging it would perhaps stop the faulty signal from reaching the computer and thus smooth out the idle, but no dice. So, I am back to thinking that something else on the intake side is causing the O2 sensor to report correctly...

      I even tried my friends MAF on my car this afternoon but again it made no difference. Next, I am going to 'borrow' my friends injectors or the entire fuel rail with injectors and FPR. I will post with the results from that in the next day or two..

      JJ







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        Intermittent Miss at Idle. 700 1987

        posted by  pbrown on  Tue Mar 18 23:58 CST 2003
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        Actually I am thinking of using these guys when I go on vacation.

        http://www.cruzinperformance.com/

        Doesn't sound like a bad deal at all. Get a new set of o-rings from the dealer box everything up and hope they get back before I do.








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          Intermittent Miss at Idle. 700 1987

          posted by  DaJet on  Wed Mar 19 07:10 CST 2003
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          last visit: Tue Jul 3 10:50 CST 2007
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          Yes, that does sound like a good deal. In regards to the O2 sensor test, I read in the FAQ last night that the voltage is supposed to jump up and down so mine is apparently good and my friends is bad..., So, I'm even more convinced now that the problem is in the injectors... Do you have a lot of miles on your car ?

          Let me know how your injectors turn out if you do decide to send them in, ok?

          Thanks,
          JJ







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