High Idle question
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Northstar Engines and System Technical Discussion Discussion, High Idle question in Cadillac Engine Technical Discussion; Ok, I got this before and thought it a fluke, but now I'm getting it ohhh...every once in a while...every ...
  1. #1
    Tailfin's Avatar
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    High Idle question

    Ok, I got this before and thought it a fluke, but now I'm getting it ohhh...every once in a while...every couple days or so, I'd say. PC0507 - high idle (seems to be around 750 - 800 warm...borderline). When I had this thing apart, I cleaned the throttle body off, I thought that might have been it, but I've done the TPS procedure, and still get it sometimes. It idles a little rough, but not bad - I still have to clean the ignition parts. My question is: Is there anything else to look out for besides the idle air control valve for the cause of this? I noticed a tiny torx screw that sets the minimum position of the throttle...but I'm assuming there's no reason this should need moving unless someone before messed with it.

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    Re: High Idle question

    When you cleaned the TB, did you get the bore as well as the throttle plate perimeter clean? How about the pivot points?

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    Tailfin's Avatar
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    Re: High Idle question

    I definitely got the bore. I'm not sure about the pivot points...but I don't think it's binding. I gave it a good soaking in B-12...

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    Re: High Idle question

    Pivot point "probably" wouldn't cause it to bind. I'm just grasping at straws.

    Did you clean the IAC valve? Other than that, the only other thing I can think of is the throttle cable or a vacuum leak.

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    Re: High Idle question

    Nope I'm about to clean the IAC. I don't think there's a vacuum leak, but I could do the starter fluid trick to be sure. My thought was the IAC being bad. I just wanted to know if I was missing something silly...or if the IAC is one of those parts that's "rarely" the problem.

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    Re: High Idle question

    Generally speaking the IAC is pretty reliable and is monitored so if it fails it should set a DTC and illuminate the MIL, BUT can't hurt to clean the pintle valve and seat. All it would take is a little carbon to hold it open a bit too much and the idle will be higher.

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    Re: High Idle question

    I had that feeling. I replaced it with a salvage yard IAC and it changed nothing. I'm suspicious of the TPS because I also have that problem of the TCC not engaging...and I've been reading my service manual. The shifting and TCC are triggered by the PCM based only on the vehicle speed and the throttle angle. If the PCM thinks the throttle is open when it's not, that would explain the TCC not engaging and not setting a code. I just need a scan tool :-P

    PS... Does something like this have the ability to manually trigger the TCC and that kind of stuff you see in the service manual?

    http://shop.advanceautoparts.com/web...Term=scan+tool

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    Re: High Idle question

    I could be wrong, but I don't think that the TPS could cause a high idle. The only thing that can cause that is more air (open throttle plate, open IAC valve or a vacuum leak.

    There may well be a link between the TPS and the TCC solenoid.

    PS... Does something like this have the ability to manually trigger the TCC and that kind of stuff you see in the service manual?

    http://shop.advanceautoparts.com/web...Term=scan+tool
    I'd rather doubt it. From what little I saw when I looked into one, they where just fancy and expensive code readers.

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    Re: High Idle question

    Yeah Ranger, I thought more about it...and the TPS should throw a code if bad too. Everytime I try to deduce what could cause the problem, I come up with stuff, but I always come back to one of them should have thrown a code. I got the high idle code fine lol. I've considered the PCM, but the car acts awfully normal otherwise for that to be on the fritz.

    I had a feeling. I know a good transmission shop I could at least take it to to diagnose it. I was just trying to avoid that if it were something I could figure out. Bloody equipment cost more than the repair :-P.

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    Roger O'Dell is offline Cadillac Owners Member
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    Re: High Idle question

    I built a 36 ford roadster and put a vvt northstar in it. Going through the tune process,every now and then my idle would mess up, took me about two years to figure out that because I had no air filter on it that when the electric fan was coming on it messed up the idle because of air from the fan. If your system is STOCK this maynot be your cause, but if modified take a look

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    Re: High Idle question

    Haha thanks for the suggestion, but no worries there on this thing. I just did the headgasket, so I"ve seen more parts of this than I cared to :-P

  13. #12
    JoeTahoe is offline Cadillac Owners Fanatic
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    I have a lot of experience with the northstars as I have done a few stud jobs. My last one had a high idle code and idled high when warm. I was pulling my hair out with this one. I have a smoke machine and could not find the problem. I finally decided to take the intake back off and look at everything. When I pulled the throttle body off there it was I put the gasket on reversed flipped it over and it ran beautiful. Just a thought.

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