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Thread: Idle adjustment question

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    Idle adjustment question

    Folks-

    My van is idling a touch low, its usually 600-650 when warm. Its been like this for a long long time but I'm now getting around to looking at the specs, and see that for my '87 LE with Auto it should be 750.

    I've got the FSM and it tells me all the stuff to do, its very straightforward. But I have one question: it says to remove the "ISC VSV" connector. Why do you need to do this? Why can't you just adjust the screw with a warm engine in neutral to 750?

    Its just that I like to know the "why" sometimes, I have no problem disconnecting the connector if need be, not like its hard to do.

    thanks!

    Mark

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    Re: Idle adjustment question

    The ISC VSV influences the idle speed at times. They just tell you to disconnect to be sure it won't mess with your adjustment. Don't mess with the throttle body stop screw. As I'm sure you know, there's a little rubber flap on the front side of the throttle body with the idle adjustment screw under it. Adjust idle speed there using a flat tip screw-driver. Tim

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    Re: Idle adjustment question

    Thanks, that totally makes sense.

    Its funny, I saw the rubber cap where the adjustment screw is, so easy to find and access, and I thought "finally, something on this van that is easy to get to"!!!!
    I'm thinking of the air filter (and so many other things) where on any other vehicle it would be so straightforward....but not on these rigs!

    Anyway we took a great trip today outside the city and I had the screwdriver up front, figured I'd set the idle while the van was good and warmed up after an hour on the road.

    I went by the FSM, they say to set idle in Neutral......the funny thing is, my idle in Neutral (and Park) is right at 750-800 (should be 750). It doesn't say anything about setting the idle in Drive.

    I put the van in Drive, it idles at 600-650. I'm giving estimates on the RPM because I didn't hook up my meter, I'm going by the dashboard, its hard to be super precise there.

    Its done this forever, its not an issue but I'm confused a little: should the idle be 750 in neutral AND Drive? Or is my idle in Drive not a problem?

    thanks!

    Mark

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    Re: Idle adjustment question

    It's completely normal for RPMs to drop to about 600 or so while in gear (automatics).

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    Re: Idle adjustment question

    I have the same kind of question. I changed 2 weeks ago the TPS on my van. Now my idle speed at "D" position (waiting at a taffic light for exemaple) is 650, but in neutral position it's 1200.

    My question is: how to adjust the idle speed? The manual show special tool to do it. Is it simply turn the idle screw under the rubber cap on the throttle body?

    my second question is: if i adjust idle speed at neutral position, does it will affect idle speed at "D" position? )

    Jerome

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    Re: Idle adjustment question

    You set it with the engine in park or neutral & AC off. Whatever RPM you see when in gear is not a big concern (unless it's stumbling or stalling). If it does that, then there's something else going on.........but no sense crossing that bridge until you come to it. Set the idle and see what happens. Tim

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    Re: Idle adjustment question

    Quote Originally Posted by timsrv View Post
    You set it with the engine in park or neutral & AC off. Whatever RPM you see when in gear is not a big concern (unless it's stumbling or stalling). If it does that, then there's something else going on.........but no sense crossing that bridge until you come to it. Set the idle and see what happens. Tim
    I'm a little confused tim, awhile ago I adjusted the idle per my service manual and I swear I read 1250 for park and 750 for drive???? Am i way too high? Was thinking it'd be nice to have it lower to avoid lurchy shifts.

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    Re: Idle adjustment question

    Quote Originally Posted by Wrench View Post
    I'm a little confused tim, awhile ago I adjusted the idle per my service manual and I swear I read 1250 for park and 750 for drive???? Am i way too high? Was thinking it'd be nice to have it lower to avoid lurchy shifts.
    Is this poster wrong? I think I might have seen this and been misinformed
    Name:  Screen Shot 2019-08-18 at 10.09.06 AM.jpg
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    Re: Idle adjustment question

    I can't read that (too small). Idle speed is set in neutral or park. The service manual calls out 700 rpm for manual transmission and 750 for automatic. It's not a super critical thing to have it right on. I would not want "hot" idle speed to be more than 900 rpm's on an automatic as this builds heat in your transmission when sitting for long periods at a light (foot on the brake while in gear). It also puts unnecessary forces on the drive train when putting it into gear from park or neutral. Tim

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    Re: Idle adjustment question

    Quote Originally Posted by timsrv View Post
    I can't read that (too small). Idle speed is set in neutral or park. The service manual calls out 700 rpm for manual transmission and 750 for automatic. It's not a super critical thing to have it right on. I would not want "hot" idle speed to be more than 900 rpm's on an automatic as this builds heat in your transmission when sitting for long periods at a light (foot on the brake while in gear). It also puts unnecessary forces on the drive train when putting it into gear from park or neutral. Tim
    Yeah rough shifts are exactly what I'm trying to avoid so I lowered it and it has indeed helped! Thanks for the clarification.

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    Re: Idle adjustment question

    Quote Originally Posted by Wrench View Post
    Is this poster wrong? I think I might have seen this and been misinformed
    Name:  Screen Shot 2019-08-18 at 10.09.06 AM.jpg
Views: 456
Size:  13.6 KB
    I just posted a reply to that thread to correct the misinformation.

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    Re: Idle adjustment question

    Thanks Original. As old as it was I was previously unaware of that post. I just searched and found that thread too. To avoid future confusion I put your edit right in that post so readers won't miss it. Since that made your post redundant I deleted it.

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    Re: Idle adjustment question

    Been working this idle issue for some time now. The main problem is that it changes when driving.
    I can set my idle for 800 RPM in park after she is up to temp, say about 15 minutes. Then I drive her for 20 to 30 minutes and when I put her in Park the idle goes up to 1300. If I shut her off and put her back on she stays at 1300. If I shut her off for 15 minutes she starts but shakes, missing at times (Heat Soak Issue). Run till past the heat soak problem and she is back at 1300. So I brought the idle down to 900 only now for the first 15 minutes of run when she is cold she idle so low she stalls.I have to feather the accelerator to keep her going. The Cold start air bypass works and raises the RPM but only for about 30 seconds and then slowing comes down to what should be idle. But she stalls since I turned the idle down when hot at 1300.

    Engine runs great, with great gas milage, better than 23mpg.

    What would cause the idle to increase so much over time? She is running very cool and is very well regulated by watching the temp gauge.
    I thought I would go get some freeze spay and shoot it at some components after she goes high on the idle just to see if I can at least localize it.

    Any thoughts?

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    Re: Idle adjustment question

    Unfortunately (or perhaps fortunately for me) I haven't experienced that problem, so I don't have any gut feelings. When I run into problems that stump me I resort to swapping parts to see what happens. I know you've already changed a bunch of stuff. If there are other things you have still not swapped, I would suggest doing so. Sorry, but without hands-on, that's the best advice I can give. Tim

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    Re: Idle adjustment question

    Quote Originally Posted by abracadabra View Post
    Why do you need to do this? Why
    Its just that I like to know the "why" sometimes, I have no problem disconnecting the connector if need be, not like its hard to do.
    Vacuum sucks, that's why.
    Check those hoses for cracks. Makes you crazy looking for the one but so satisfying when a new rubber hose fixes it.

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    Re: Idle adjustment question

    Again, thanks for the feedback.

    All rubber hoses been replaced. I did find a crack in my EGR tube that mounts below on the exhaust manifold and I thought that was it. But I still cannot figure this on out. I do believe it is a vac problem still. Today I am going to pick up some starter fluid (Ether) and shoot those vac junctions. I may find one that is leaking still. There are tons of them, who knows. I will stay away from anything that can ignite this stuff.

    If it is a thermal issues it has to be located somewhere on top, like the mixture control assembly or any of the sensors not senders. Anything that has a variable input to the MCU may can also be a culprit. I will also pick up some freeze spay and shoot all the parts after it is up at high idle speed. I know it does not change even if I have the engine cover open for some time. It never goes down until she is really cold like less than 100 deg or so.

    If all else fails I will mount on the engine a bunch of temp probs to see if anything in particular looks funny at different operation temps.

    Will keep you posted.

    MT

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    Re: Idle adjustment question

    MT - You can use ether and it works just fine but I find it harder to control as it usually under significant pressure, tends to spray all over.
    These days I use a propane torch, easy to control the flow and I find its better for pin-pointing leaks.

    I also choose to believe its a little safer, mostly because I can control the amount I use as opposed to a blast here and a blast there.
    I once had an exhaust leak ignite ether, it was quite the experience and why I now use propane - YMMV

    BB

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    Re: Idle adjustment question

    Many things will work. I've even used carb cleaner and WD-40 (although I don't recommend WD-40 due to the residue mess). I've also had ether accidentally ignite and although scary, it was just a flash fire and was gone almost as soon as it started. It did however burn long enough to take some arm hair . Tim

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    Re: Idle adjustment question

    OK, I will watch myself. I have a small portable propane for fixing plumbing stuff. So I can just turn on the gas and point it to the areas I want to test and it will race if it is leaking like the ether?
    Cool, I will give it a go.

    MT

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    Re: Idle adjustment question

    A bit of an update on this.
    I tried the propane, hey look at me? I am still alive and kicking!

    Anyway it did not show anything.
    Since it runs so rough under 800 rpm no matter what temp she is resting at I decided to pull the plugs and take a look at the way they are burning.
    As you can see by the pic they are all the same and they are seem to be very light tan.
    Could this be that they are burning to lean?
    Then through in the temp senders job. For sure its resistance reporting to the MCU must control its mixture, low resistance lean and high resistance rich. Just a guess.

    So I tried just yanking the temp connector off while it was running, hot at this point, high idle rpm.

    Did nothing except forced my check engine light to come on.

    Checked the sender and when hot it is at 408 ohms and cold it is 20,0000

    So the temp sender is working and not doubt linear also.
    So my next question is if the MCU is the problem?
    To do this I will pull the MCU and check for continuity to the temp sender and make sure there is no issue there.
    If OK, which it most likely will be, I will build an outside potentiometer that can slide between 20K and 200 ohms. In theory I should be able to set that for 20K, start the engine and slide it down to 200 ohms and she should do something, like stall from being too lean. If I get no response at all then the MCU is the problem.

    Any comments?
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