4.1L Idle Speed Issues
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HT4100 4.1, 4.5, 4.9 Discussion, 4.1L Idle Speed Issues in Cadillac Engine Technical Discussion; Right. I have a 1985 Fleetwood Brougham RWD with the 4.1 engine. After having a few things fixed at a ...
  1. #1
    TheRedSharon's Avatar
    TheRedSharon is offline Cadillac Owners Member
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    4.1L Idle Speed Issues

    Right. I have a 1985 Fleetwood Brougham RWD with the 4.1 engine. After having a few things fixed at a mechanic a few months ago, I've noticed that my car idles at different speeds. Sometimes its barely audible, sometimes it sounds like I'm horsing the engine, and it flies up to 45mph if I give it gas. Thing is, I've been driving the car and felt it change from a high idle to a lower one. Does anyone have a clue? I'm wearing out my brakes.

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    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.1L Idle Speed Issues

    I think you're looking at an ISC replacement or adjustment. You also need to rod out the EGR tubes in the intake manifold just below the throttle body butterflies.

    Drew was right, we need to post stickies on the common problems to these engines...

  4. #3
    TheRedSharon's Avatar
    TheRedSharon is offline Cadillac Owners Member
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    Re: 4.1L Idle Speed Issues

    Quote Originally Posted by the recluse View Post
    I think you're looking at an ISC replacement or adjustment. You also need to rod out the EGR tubes in the intake manifold just below the throttle body butterflies.

    Drew was right, we need to post stickies on the common problems to these engines...
    I already paid for a new ISC, so I'm hoping that's not the problem. How difficult would it be to rod out the EGR tubes?

  5. #4
    OffThaHorseCEO is offline Cadillac Owners Connoisseur
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    Re: 4.1L Idle Speed Issues

    was the re-learn procedure necessary on these 4.1's

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    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.1L Idle Speed Issues

    Quote Originally Posted by TheRedSharon View Post
    How difficult would it be to rod out the EGR tubes?
    Not hard at all. just push open the butterflies and you'll be looking at the tubes. Take a wire coat hanger and run it up and down to break up as much of the carbon build up you can. I also use some carb cleaner maximize cleaning.

    IIRC, no, the relearn was not needed, it just worked. Did your mechanic check the TPS adjustment? He should've at the same time he put on the ISC motor. A mal-adjusted TPS will also give you fits...

    HTH

  7. #6
    TheRedSharon's Avatar
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    Re: 4.1L Idle Speed Issues

    Quote Originally Posted by the recluse View Post
    Not hard at all. just push open the butterflies and you'll be looking at the tubes. Take a wire coat hanger and run it up and down to break up as much of the carbon build up you can. I also use some carb cleaner maximize cleaning.

    IIRC, no, the relearn was not needed, it just worked. Did your mechanic check the TPS adjustment? He should've at the same time he put on the ISC motor. A mal-adjusted TPS will also give you fits...

    HTH
    He might have said something about a TPS, but it got lost with the talk of the ISC. Would a bad TPS adjustment cause a car to choke down when the accelerator is pressed?

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    the recluse is offline Cadillac Owners Connoisseur
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    Re: 4.1L Idle Speed Issues

    Quote Originally Posted by TheRedSharon View Post
    Would a bad TPS adjustment cause a car to choke down when the accelerator is pressed?
    Yuuuup Can also be a bad MAP sensor, but the TPS is only an adjustment check and is free. Try that first and let me know.

  9. #8
    drewsdeville is offline Cadillac Owners Master
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    Re: 4.1L Idle Speed Issues

    FWIW, the idle learn is NOT necessary. The pcm will learn the idle through regular driving/use, which really doesn't take long. The procedure simply accelerates the process.

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    TheRedSharon is offline Cadillac Owners Member
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    Re: 4.1L Idle Speed Issues

    So Recluse, you were right. My TPS was malfunctioning, and I took an hour one Saturday to replace it. Minimal work, and my problem was solved.

    Well, at least the varying idle speeds. Now I've got an even worse problem: my car doesn't want to start. I was going to take it to the mechanic last week (for a completely unrelated issue) when I found she wouldn't catch. They told me that my distributor cap had been messed up by the last guy who worked on it. I paid for the work, headed home to change for work, and when I came back out, the damn car wouldn't even start. Whereas before, I could hear things turning, now it'll turn once or twice and stop.

    I experimented with it this afternoon, and as far as I can tell, the car doesn't want to start before ten to twenty minutes after being driven. Ideas?

  11. #10
    drewsdeville is offline Cadillac Owners Master
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    Re: 4.1L Idle Speed Issues

    Quote Originally Posted by TheRedSharon View Post
    So Recluse, you were right. My TPS was malfunctioning, and I took an hour one Saturday to replace it. Minimal work, and my problem was solved.

    Well, at least the varying idle speeds. Now I've got an even worse problem: my car doesn't want to start. I was going to take it to the mechanic last week (for a completely unrelated issue) when I found she wouldn't catch. They told me that my distributor cap had been messed up by the last guy who worked on it. I paid for the work, headed home to change for work, and when I came back out, the damn car wouldn't even start. Whereas before, I could hear things turning, now it'll turn once or twice and stop.

    I experimented with it this afternoon, and as far as I can tell, the car doesn't want to start before ten to twenty minutes after being driven. Ideas?
    As usual, start by eliminating fuel or spark as the intermittent problem is one of the two. Easiest way is to spray a shot of starting fluid down the throttle body and try it again. If it starts, the problem is fuel. If it doesn't, spark is the problem.

  12. #11
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    Re: 4.1L Idle Speed Issues

    Did you adjust the TPS after installing it? I believe if it's far enough out of range, the computer will think you have the gas pedal pressed down during startup and will deny fuel to the engine to prevent flooding. Just a hunch... although I would assume that you'd have major driveability issues if it was that far out...

  13. #12
    TheRedSharon's Avatar
    TheRedSharon is offline Cadillac Owners Member
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    Re: 4.1L Idle Speed Issues

    @DrewsDeville: Starting fluid? What is that? I took the air cleaner off the other day and I could see (what I believe is) fuel spraying into the throttle body. After holding the accelerator lightly for a moment or two, when I released it the spray would nearly stop before going back to normal.
    @Sevillian273: I did not adjust the TPS after installation. After I put it on however, every time I started the car it would run just fine and I had no trouble starting it. I drove it one night on a twenty mile round trip with no problem.

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