1994 Cadillac Deville High Idle
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HT4100 4.1, 4.5, 4.9 Discussion, 1994 Cadillac Deville High Idle in Cadillac Engine Technical Discussion; Hey guys, I'm having an issue with the 94 cadillac sedan deville 4.9. I just recently had some work done ...
  1. #1
    soulman07 is offline Cadillac Owners Member
    Automobile(s): 1994 Cadillac Sedan Deville
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    1994 Cadillac Deville High Idle

    Hey guys, I'm having an issue with the 94 cadillac sedan deville 4.9.

    I just recently had some work done on it and I don't even begin to know where to list all the things that have been replaced.

    Heads were rebuilt @120k, mounts, FPR, EGR, plugs, wires,cap,tie rod ends, sway bar end links, front struts, rear coil overs, knuckles...

    The list goes on. Only reason why I decided to invest such money into a car is because it belonged to my brother who was murdered August 16th of last year. So thing old cadillac means quite a bit to me.

    The only issue I'm having really is the idle speed of it. Just recently I replaced the EGR gasket that was on the car because I was getting some noise which i originally thought was from the exhaust manifold. I took both manifolds out and drilled wider holes that the standard 5/16 put a bolt in the back of each and torqued them down where they connect into the exhaust pipe to fix the issue. Still was loud revving from accelerating on a dead start afterwards. So I did some additional search and I found that the noise was coming from the EGR. I got the new gasket placed some gasket maker on it and replaced it let it dry and revved it up a few times and now it's all sounding good. I removed the line that connects to the MAP sensor on the car at the time and the piece of vaccum that connects it to the intake was like rock solid and I didn't actually notice it being cracked until the following day when I got home from work. The car would kill on idle, It's been replaced and all is well now. It's idling high when you start it from time to time, It's not a constant thing though. Driving down the freeway I can feel the accelerator going down like I'm pressing on it and maintaining a desired speed and then coming back up again... Which leads me to believe that it may be an issue going on with the cruise control. The gas pedal goes down then back up then repeats the same motion. The engine is revving itself up and down in the midst of it all too.

    Any help is greatly appreciated,

    Terence

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  3. #2
    79malibuonblocks is offline Cadillac Owners Member
    Automobile(s): 1984 coupe deville 4.1 67,000original/1991 sedan deville 4.9
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    Re: 1994 Cadillac Deville High Idle

    check for vacume leaks.........buddy had a 96 seville, had a vaccume leak, causin to to idle at full speed.

  4. #3
    Rodya234's Avatar
    Rodya234 is offline Cadillac Owners Connoisseur
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    Re: 1994 Cadillac Deville High Idle

    Have you done the idle learn procedure? This fixed the idle problems with my sisters '93 and is very quick, simple, and it's free.

  5. #4
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 1994 Cadillac Deville High Idle

    Other than your foot, the cruise control diaphragm is the only thing that can move the gas pedal. It is powered by engine vacuum so disconnect the vacuum line going to it and cap it off, then see if it happens anymore. Or you can disconnect the cable going from it to the throttle body.

  6. #5
    pompste is offline Cadillac Owners Connoisseur
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    Re: 1994 Cadillac Deville High Idle

    Quote Originally Posted by soulman07 View Post
    Hey guys, I'm having an issue with the 94 cadillac sedan deville 4.9.

    I just recently had some work done on it and I don't even begin to know where to list all the things that have been replaced.

    Heads were rebuilt @120k, mounts, FPR, EGR, plugs, wires,cap,tie rod ends, sway bar end links, front struts, rear coil overs, knuckles...

    The list goes on. Only reason why I decided to invest such money into a car is because it belonged to my brother who was murdered August 16th of last year. So thing old cadillac means quite a bit to me.

    The only issue I'm having really is the idle speed of it. Just recently I replaced the EGR gasket that was on the car because I was getting some noise which i originally thought was from the exhaust manifold. I took both manifolds out and drilled wider holes that the standard 5/16 put a bolt in the back of each and torqued them down where they connect into the exhaust pipe to fix the issue. Still was loud revving from accelerating on a dead start afterwards. So I did some additional search and I found that the noise was coming from the EGR. I got the new gasket placed some gasket maker on it and replaced it let it dry and revved it up a few times and now it's all sounding good. I removed the line that connects to the MAP sensor on the car at the time and the piece of vaccum that connects it to the intake was like rock solid and I didn't actually notice it being cracked until the following day when I got home from work. The car would kill on idle, It's been replaced and all is well now. It's idling high when you start it from time to time, It's not a constant thing though. Driving down the freeway I can feel the accelerator going down like I'm pressing on it and maintaining a desired speed and then coming back up again... Which leads me to believe that it may be an issue going on with the cruise control. The gas pedal goes down then back up then repeats the same motion. The engine is revving itself up and down in the midst of it all too.

    Any help is greatly appreciated,

    Terence
    Sorry to read about your brother--- i can see why the Caddy means a lot to you.
    Follow the others advice and check for any codes.

  7. #6
    soulman07 is offline Cadillac Owners Member
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    Re: 1994 Cadillac Deville High Idle

    Only two codes I have PO91 and PO40 40 has something to do with power steering and 91 I'm not sure about. I tried the idle learn procedure yesterday and it didn't help any, still having the same issues as I stated before.

    It's the part below that the metal piece sticks out from that goes in an out and in an out intermittently from time to time and causes my gas pedal to go up and down and also to ping in acceleration. Could this also be the reason for it idling high?

    I plan on replacing it tomorrow, I'd like to know the part name but I'm having issues locating it on rockauto.com.

    Thanks again for the kindness folks.
    Attached Images

  8. #7
    79malibuonblocks is offline Cadillac Owners Member
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    Re: 1994 Cadillac Deville High Idle

    Quote Originally Posted by soulman07 View Post
    Only two codes I have PO91 and PO40 40 has something to do with power steering and 91 I'm not sure about. I tried the idle learn procedure yesterday and it didn't help any, still having the same issues as I stated before.

    It's the part below that the metal piece sticks out from that goes in an out and in an out intermittently from time to time and causes my gas pedal to go up and down and also to ping in acceleration. Could this also be the reason for it idling high?

    I plan on replacing it tomorrow, I'd like to know the part name but I'm having issues locating it on rockauto.com.

    Thanks again for the kindness folks.
    Thats the A/C idle up- sylanoid. Not the proper term, but when u turn the A/C on it engages it and idles the car up to compensate for the load the A/C compressor puts on the motor. You can adjust it by screwing it in to back it off(idle down) or screw it out to idle up. But disconnect the wires to it first, make sure the plunger is not touchin the throttle bracket and see if it helps.

  9. #8
    79malibuonblocks is offline Cadillac Owners Member
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    Re: 1994 Cadillac Deville High Idle

    e 91 is the PRNDL switch problem. Might be the same thing.

  10. #9
    soulman07 is offline Cadillac Owners Member
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    Re: 1994 Cadillac Deville High Idle

    I did a little bit of research and the valve is called the *Idle Air Control Valve* it's what opens the throttle enough for the car to idle at the desired RPM. Has nothing to do with the A/C itself. It's about a 100 dollar replacement part brand new and I've seen instances where it's been built up with gunk and just needed cleaning too. I'll see about getting it cleaned up tomorrow and if it fixes the problem. If not I'll purchase a new one, I'll keep you guys posted

  11. #10
    soulman07 is offline Cadillac Owners Member
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    Re: 1994 Cadillac Deville High Idle

    Anyone one know where the *Power Steering Pressure Switch* is located? I'm having a hard time finding it... Even though I know what it looks like

  12. #11
    79malibuonblocks is offline Cadillac Owners Member
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    Re: 1994 Cadillac Deville High Idle

    Quote Originally Posted by soulman07 View Post
    I did a little bit of research and the valve is called the *Idle Air Control Valve* it's what opens the throttle enough for the car to idle at the desired RPM. Has nothing to do with the A/C itself. It's about a 100 dollar replacement part brand new and I've seen instances where it's been built up with gunk and just needed cleaning too. I'll see about getting it cleaned up tomorrow and if it fixes the problem. If not I'll purchase a new one, I'll keep you guys posted
    What you are showing in that pic is not the IAC valve, the IAC valve threads into the throttle body and acts as a choke.

  13. #12
    soulman07 is offline Cadillac Owners Member
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    Re: 1994 Cadillac Deville High Idle

    Hmm, It's listed under that at www.rockauto.com, I found a junkyard replacement for 6.00 and attached it there and replaced all of the existing vacum and she's back to purring like a kitten and idling smooth. Still getting codes on the dash for the power steering switch. The replacement for it is around 26.00 and I have no idea where to look. I've looked all throughout the engine bay, Only switch i located was the sensor for oil pressure.

    Any idea where to look?

  14. #13
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 1994 Cadillac Deville High Idle

    My haynes manual says its on the steering gear. It lets the ECM know when your turning the wheel so it can raise the rpm to accomodate for the load.

  15. #14
    79malibuonblocks is offline Cadillac Owners Member
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    Re: 1994 Cadillac Deville High Idle

    Cadillac's and all their extra "luxury" stuff....LOL. Man have u seen the power steering cooler under the passenger floorboard? It's there, whats the sense in that?

  16. #15
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 1994 Cadillac Deville High Idle

    P/S cooler?? I didnt know there was one. Ill have to check that out tomorrow..... I was really surprised to find that there was a factory oil cooler on my Seville. Gotta love Cadillac!

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