This is another area where the Maxima ECU strategy seems more "finicky" than what I am used to on GM. I think I need to perform this, because I think the hot neutral idle speed is supposed to be like 625rpm and most of the time, it's higher than that (every once in a while it goes to 625 and it's perfectly smooth and almost silent even with the fart can).
It looks like the procedure is basically hold rpms steady, then idle it, then disconnect TPS, then rev it, then idle it...then reconnect TPS. There is actually an idle speed adjustment, which is wacky on EFI, though it seems you only have to do that if the timing is wrong (the expectation is that the idle speed should be correct if the timing hasn't been changed?). Certainly timing will affect idle speed but I don't think it's the only cause. I guess if the idle isn't 575 with the TPS disconnected I'll look at it.
Maxima idle speed setting
Maxima idle speed setting
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Re: Maxima idle speed setting
I finally got around to performing this adjustment. Happily for me, I was right - it needed it. I did not check the timing because I have no reason to believe it's set improperly. Not to mention, incorrect timing means something is actually broken (there is no adjustment or setting). And I don't think anything is broken.
Anyway, I followed the directions. You're supposed to hold it at 2k for 2 minutes then rev it a few times, then shut it down. Disconnect TPS harness. Start back up (engine sees 100% TPS so idle was elevated). Then turn the adjustment screw on the IACV until idle is 575rpm +/- 50rpm. Interestingly, I had to turn in the adjustment until it bottomed out, to get the idle down to 575 or 600. I'm not sure that's how it's supposed to work. Perhaps there is a vacuum leak. It's not the IACV gasket or any of the EGR stuff as I replaced all those gaskets.
Throttle body gasket? Misc vacuum leak? I don't hear anything. Maybe there's a throttle stop adjustment (manual doesn't mention it in the idle adjustment section). Anyway, at least I got it to spec. Then I shut it off, plugged the harness back in, and restarted it. It now properly idles down to 625rpm +/- 50 in neutral. It's really quiet even with the exhaust.
Another fallout of having the IACV air bypass setting correct is that transition in and out of DFCO is now VERY smooth. That makes sense as there's less bypass air when the throttle is closed, so engine braking has decreased a bit. Then when fuel cuts back in, there's less airflow to cause a torque surge. In other words, it's driving like it's supposed to. Despite the mechanical engine mount lash, this is a very refined engine, I maintain. Part of my attraction to it is that it goes about its business with a simplicity of a Gen III+ SBC (no variable anything, just overhead cams). Well, as far as you can expect simplicity from a Japanese engine like this. Some of the engine controls are still more complicated than I think they need to be.
Side note, I checked the long term fuel trims while driving. They went as high as 10%, but no higher. I dunno if that proves there's some small vacuum leak or not. Drivability seems perfect so I say it's fixed.
Anyway, I followed the directions. You're supposed to hold it at 2k for 2 minutes then rev it a few times, then shut it down. Disconnect TPS harness. Start back up (engine sees 100% TPS so idle was elevated). Then turn the adjustment screw on the IACV until idle is 575rpm +/- 50rpm. Interestingly, I had to turn in the adjustment until it bottomed out, to get the idle down to 575 or 600. I'm not sure that's how it's supposed to work. Perhaps there is a vacuum leak. It's not the IACV gasket or any of the EGR stuff as I replaced all those gaskets.
Throttle body gasket? Misc vacuum leak? I don't hear anything. Maybe there's a throttle stop adjustment (manual doesn't mention it in the idle adjustment section). Anyway, at least I got it to spec. Then I shut it off, plugged the harness back in, and restarted it. It now properly idles down to 625rpm +/- 50 in neutral. It's really quiet even with the exhaust.
Another fallout of having the IACV air bypass setting correct is that transition in and out of DFCO is now VERY smooth. That makes sense as there's less bypass air when the throttle is closed, so engine braking has decreased a bit. Then when fuel cuts back in, there's less airflow to cause a torque surge. In other words, it's driving like it's supposed to. Despite the mechanical engine mount lash, this is a very refined engine, I maintain. Part of my attraction to it is that it goes about its business with a simplicity of a Gen III+ SBC (no variable anything, just overhead cams). Well, as far as you can expect simplicity from a Japanese engine like this. Some of the engine controls are still more complicated than I think they need to be.
Side note, I checked the long term fuel trims while driving. They went as high as 10%, but no higher. I dunno if that proves there's some small vacuum leak or not. Drivability seems perfect so I say it's fixed.
Re: Maxima idle speed setting
It does have a throttle stop adjustment. I can't find anything in the FSM about it. Theoretically I could back off to let the throttle close more, which should require the IACV bypass to be opened up. That way, everything's in better balance. But I don't think I'm going to bother. At least not at the moment. Off the top of my head, I could have throttle sticking issues, even though I've cleaned the TB.
Oh, as a result of the lower (correct) idle speed, I stalled the car at a light already. An 850-900rpm idle is a lot easier than a 625rpm idle, unless you want to slip the shit out of the clutch (which I don't).
Oh, as a result of the lower (correct) idle speed, I stalled the car at a light already. An 850-900rpm idle is a lot easier than a 625rpm idle, unless you want to slip the shit out of the clutch (which I don't).
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Re: Maxima idle speed setting
Well this is funny. I went to start the Maxima an hour ago to return a Netflix movie. It cranked, fired, and stalled. Did that like 4 times. I ended up giving it gas to nurse the idle for a couple seconds. So that bypass air isn't enough for the IACV to handle the load of cold oil and a cold trans. Once I stabilized the idle I let the clutch out, and that almost killed it again. This is what my brother was complaining about when he drove it, I think. I might assume he brought the car somewhere and they adjusted that knob out a bunch of times to prevent the stalling...but I don't think he brought the car anywhere.
I opened up the bypass air valve a bit. I think the answer is to find the conditions where the IACV would be almost closed, which would be hot engine, hot oil, hot trans and a 625rpm idle. I could turn the adjustment open until the IACV can't close and control the idle (i.e. open it until the idle starts to pick up from 625rpm and won't decrease).
This explains why, before, I would see the correct idle under certain conditions. Those conditions were an engine that wasn't fully warmed up, so there was enough drag to keep the idle down. But as the oil warms up, the drag decreases, and it became evident that the bypass air was too much and I assume the IACV was closed all the way. Or it's starting to fail.
It is going to be 18°F when I start the Maxima tomorrow morning. I bet my adjustment wasn't enough. We'll see.
I opened up the bypass air valve a bit. I think the answer is to find the conditions where the IACV would be almost closed, which would be hot engine, hot oil, hot trans and a 625rpm idle. I could turn the adjustment open until the IACV can't close and control the idle (i.e. open it until the idle starts to pick up from 625rpm and won't decrease).
This explains why, before, I would see the correct idle under certain conditions. Those conditions were an engine that wasn't fully warmed up, so there was enough drag to keep the idle down. But as the oil warms up, the drag decreases, and it became evident that the bypass air was too much and I assume the IACV was closed all the way. Or it's starting to fail.
It is going to be 18°F when I start the Maxima tomorrow morning. I bet my adjustment wasn't enough. We'll see.
Re: Maxima idle speed setting
The idle when I got home seemed to want to be around 650. I found the most backed out bypass air setting that put me around 663 or so...we'll see how it behaves. It may have to learn the new IACV positions. Or I could disconnect the battery and let it re-learn. Did I mention this car also has a throttle kicker for the A/C? So much complexity. What is this, a German car?