Lurching idle
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Northstar Engines and System Technical Discussion Discussion, Lurching idle in Cadillac Engine Technical Discussion; For several weeks now my 2008 N* has been idling poorly. For a lack of a better word it is ...
  1. #1
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    Lurching idle

    For several weeks now my 2008 N* has been idling poorly. For a lack of a better word it is lurching at idle. In gear or park doesn't matter. But it is more pronounced in gear. The rpm doesn't change but it feels like the car wants to start driving on its own. These are brief occurances but frequent. Once I give it throttle all is fine. Since I thought it seemed like a vacuum leak I have already changed the intake plenum, intake manifold gaskets, MAP sensor, also changed the crankshaft position sensor, both knock sensors, camshaft position sensor, wiring harness for these sensors, thorughly cleaned the throttle body and the EGR and the MAF. Next on tap is to change the throttle body gasket. I also bought 4 injectors to swap out a side at a time. This issue still persists and I am wondering if I am missing something. Any help would be appreciated. Thanks
    Don

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    Submariner409's Avatar
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    Re: Lurching idle

    Don ........... Long shot, but what about a bad resistance strip in the TPS ? The PCM could be "hunting" for an idle reference.

    ............ but the "no rpm change" thing is a mystery.

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    Re: Lurching idle

    Yeah I know right. I think I am going to do the gasket change and injector swap and if I still get nowhere it is time to have the dealer check it out. I just know that it is gonna cost a metric ton to have it fixed there. And that is if they diagnose it right the first time.

    Don

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    Re: Lurching idle

    No DTC's?

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    Re: Lurching idle

    No DTC's. That is what is killing me. This is one time I was praying for a code to set. Anyway I changed the throttle body gasket today. Also cleaned the throttle body AGAIN. Damn they get dirty fast. But no change. I then swapped the four right side (rear) injectors. Although it feels like the issue is resolved I will hold elation until driving the car a few days. Once before I thought it was repaired only to have the issue resurface.

    Does anyone know it the injectors has a bench test procedure? Like a resistance check? Or do they need to be on the vehicle to test them? I have a DVD repair manual and the test procedures listed are either on the vehicle or with some fancy test equipment that I do not own. But a simple resistance check I can do. Would be nice to know if one or more injectors are just dirty needing cleaning or faulty

    Don

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    Re: Lurching idle

    I think our injector coil resistance should be 11 - 14 Ohms.

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    Re: Lurching idle

    Quote Originally Posted by Submariner409 View Post
    I think our injector coil resistance should be 11 - 14 Ohms.
    But is that a bench test procedure or an on the car one? The manual I have kind of makes it seem that you use the Tech 2 for that. Just wondering

    Don

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    Re: Lurching idle

    An unplugged injector should measure XX Ω across the two terminals either in the manifold or on the bench.

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    Re: Lurching idle

    Okay so I changed out the 4 injectors and my problem is 90% cured. Do not want to deal with this anymore so I am buying 4 more. Anyway I tested the 4 old ones. Three of the tested at 11.9-12.3 ohms. The other one went between 11.9 and infinity. Couldn't get it to stay in spec for more than 10 seconds or so. It was bouncing all around. Then I decided to check the other four that I didn't change. Since I had just drove the car the engine was hot. All four tested at about 14.8 or so. I am guessing because of the heat. Also didn't keep the multimeter on there too long because of the heat so I couldn't check for variances over time. Anyway there are 4 more injectors in my future. I will post again once I get them and install them.

    Don

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    Re: Lurching idle

    WOW! Injectors are pretty reliable. I'm surprised to hear that.

  12. #11
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    Re: Lurching idle

    Me too. I would have bet the farm it was a vacuum leak. Injectors didn't even cross my mind. Hoping that changing the other four makes the issue 100% fixed.

    Don

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    Re: Lurching idle

    Ended up being a severe misfire on cylinder 8. And a miniscule misfire on cylinder 1. Dealer installed a good used coil in 8 and the issue is 99% gone. So I bought two coils and when they arrive I will install them in 1 and 8. I will return the used coil to the dealer. But finally it is nice to have a properly functioning Cadillac again

    Don

  14. #13
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    Re: Lurching idle

    Replacing coils 1 and 8 fixed the issue. Engine runs butter smooth again.

    Don

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    Re: Lurching idle

    The individual coils on newer cars die all the time. Beauty covers covering everything and they don't help dissipating heat. Plastic is a lousy thermal conductor. And in most cases they even have those sound deadening material, which also provides a good heat insulation...

    I have seen several cars having dead coils within a few years, most of them having individual coils on plug covered by engine beauty covers. Never had any problem with exposed 99 coil packs, or 00 ICM with heat sinks.

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    Re: Lurching idle

    Funny you mention that Harry... according to the previous work history on my Deville a few of the coil packs have already been replaced. It was the same situation with my BMW as well.

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