Rough Idle. Can't figure it out... 1994 STS
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Rough Idle. Can't figure it out... 1994 STS in Past Cadillac Vehicle Discussion; Ok here we go,Ii'll try to give all the info I can think of . Car info : 1994 cadillac ...
  1. #1
    cliff77 is offline Cadillac Owners Member
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    Question Rough Idle. Can't figure it out... 1994 STS

    Ok here we go,Ii'll try to give all the info I can think of .
    Car info : 1994 cadillac sts 4.6 northstar 145,000 miles
    new parts:
    4 new coil packs
    plug wires
    plugs
    air filter
    fuel filter

    Here's what the car is doing.
    Rich feeling: Idles a little rough, you can smell gas / unused fuel at the exhaust tips. Gas milage is lower than expected (14.6 interstate). Litte sluggish off the line, runs good at crusing speed, but misses when in overdrive and the speed is around 50. (very powerful while moving).
    No codes showing except 2 suspension codes (air bags are blown) and the memory lose code (disconnected battery)

    It's been to local car mechanic, only thing he came up with is bad convertor (he was guessing I think). Dealer said bad vacuum leak at vacuum manifold ? I did find what he was talking about. It's the connector on the top of throtle body that has 3 vacuum hoses coming out of it. it's cracked and is sucking air.
    Dealer said that part is not made anymore and they can't find it anywhere. I haven't looked I just got the car back yesterday afternoon.So I figured I would start here.
    But I have always understood vacuum leak creates lean enviorment, not a rich one.IDK

    Any help, would be great !!

    P.S. I have owned another 94 sts caddy, same age, same car. so I know what this one is doing ins't right. The other one did have fuel problems too, but they were egr related.

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    MoistCabbage's Avatar
    MoistCabbage is online now Cadillac Owners 10000+ Posts
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    Has anyone tested the fuel pressure regulator?

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    vincentm's Avatar
    vincentm is offline Cadillac Owners Connoisseur
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    ^That

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    cliff77 is offline Cadillac Owners Member
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    Re: Can't figure it out... please help !!!!

    next on the list

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    Re: Can't figure it out... please help !!!!

    My money is on the FPR as well.

    As for the vacuum port, you may have to improvise.

    P.S.
    I edited you title to be a little more descriptive.

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    cliff77 is offline Cadillac Owners Member
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    Re: Rough Idle. Can't figure it out... please help !!!!

    I fixed (remade) the vacuum manifold/port.
    Helped a very little bit, nothing inpressive.
    Where is the fuel pressure regulator at ?






    |

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    MoistCabbage's Avatar
    MoistCabbage is online now Cadillac Owners 10000+ Posts
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    On a '94, under the aluminum intake cover.

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    cliff77 is offline Cadillac Owners Member
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    Re: Rough Idle. Can't figure it out... please help !!!!

    ok, I'll go get it and give it a try..... Thanks

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    MoistCabbage's Avatar
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    Well it's not just that simple. Have you ever had the cover off before? Do you have a torque wrench to reinstall it?

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    cliff77 is offline Cadillac Owners Member
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    Re: Rough Idle. Can't figure it out... please help !!!!

    Fuel pressure reg replaced. I can't tell a big difference. but I haven't drove it but around the block. Will it take awhile for the computer to reconize it ?

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    MoistCabbage's Avatar
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    No, it's a mechanical regulator, no computer involved.

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    cliff77 is offline Cadillac Owners Member
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    Re: Rough Idle. Can't figure it out... please help !!!!

    Ok, what I meant was, will I need to put some miles on it before the computer recognize the different fuel pressure (if any)

    where to go next ? I don't have anymore ideas.....

  14. #13
    MoistCabbage's Avatar
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    No, fuel pressure isn't monitored.

    Leaking/sticking fuel injector?

  15. #14
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    Re: Rough Idle. Can't figure it out... please help !!!!

    Iirc, the obd1 models include the ability to view pcm data. Using that, you should be able to narrow things down to begin troubleshooting rather than trying this and that...

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    Re: Rough Idle. Can't figure it out... please help !!!!

    A little late now, but there was no need to replace the FPR unless it was leaking. You should have inspected it before throwing parts at it. That gets expensive in a hurry.

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