Engine revving on its own
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Northstar Engines and System Technical Discussion Discussion, Engine revving on its own in Cadillac Engine Technical Discussion; I recently purchased an imaculate 1993 sts with the 4.6l from a little old lady that didn't want it anymore ...
  1. #1
    Dvandy1 is offline Cadillac Owners Member
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    Engine revving on its own

    I recently purchased an imaculate 1993 sts with the 4.6l from a little old lady that didn't want it anymore and I need help with it. When I bought is she said that one day she went out to start it would just idle up and up and she would have to turn it off. Well, when I got it home I started it and it fired up and it immediatly jumped to 2200 rpm and then every couple of second it would just keep climbing after about 10 or 15 seconds it jumped to about 5000 rpm and the headers started glowing because I'm guessing it was running lean so I quickly shut it down...any suggestions? It ran smooth while it was running and there are no codes in it except from trying to reset it by disconnecting the batt. Any help or suggestions would be greatly appreciated

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    ejguillot's Avatar
    ejguillot is offline Cadillac Owners Enthusiast
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    Re: Engine revving on its own

    I would look for a vacuum leak if I were you. Make sure that all the seals are doing their job, including the intake plenum cover (don't try to run the engine without it, it will run away unthrottled).

    Fix all the vacuum leaks, then get back to us with an update.

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    Dvandy1 is offline Cadillac Owners Member
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    Re: Engine revving on its own

    I was thinking that should be my next step. I took off the air cleaner tube and cupped my hand over the opening and it didn't phase the rpm at all so its got to be getting air from somewhere.....

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    Dvandy1 is offline Cadillac Owners Member
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    Re: Engine revving on its own

    I found the probem the side of the intake has about 2 or 3 arge cracks in it. Im guessing that I may have drippy injector that caused a backfire......anyone have any suggestions?

  6. #5
    ejguillot's Avatar
    ejguillot is offline Cadillac Owners Enthusiast
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    Re: Engine revving on its own

    Are the cracks you found after, or before the throttle body? If before, that shouldn't make the RPM shoot up like that. Keep looking (do fix those cracks, then see if the RPM situation improves).

    Have you accounted for all the vacuum hoses?

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Engine revving on its own

    Replace the intake.

  8. #7
    Dvandy1 is offline Cadillac Owners Member
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    Re: Engine revving on its own

    I found 2 decent size cracks on the pass side of the intake. One of the cracks is a good 1/16 to 1/8 open so I'm sure thats enough of a vac leak for a couple engines. I found a place near me in MI to ship a good used intake with injectors and wires for $100. I guess I'll test the other injectors before putting it on, but other than that I think it should work.

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