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nmehdikh

240z with L26 - ITBs, EFI, megasquirt

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I got in a new IAC, but haven't had a chance to mess with it yet. I'll try your suggestion this weekend, thanks for the input. My bigger issue is that I wasn't really getting any change in idle speed regardless of the position of the idle valve, which leads me to believe I may have a vacuum leak to hunt down as well.

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On 1/22/2019 at 12:29 PM, rossman said:

It looks like gaps on either side of the valve at 35%.  At 0% there is a gap on the right but none on the left. It looks defective to me.

 

This is exactly how it should operate. The valve body is barrel shaped. at 0% the internal spring is relaxed. when the voltage goes up (duty cycle increases) the barrel will turn to the right. at first the right side is open, then it will close up, and then it will start to open on the left side.

I use a similar air valve like this with a simple $15 chinese PWM power suply. works great. I can adjust the idle rpm with a small dashpot on the center console.

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I'm really scratching my head over this. I swapped out the IAC with a new one. Car idles stable at 550 rpms, but regardless of what the IAC is doing, the RPMs don't change. The valve is physically opening and closing when commanded by the ECU. (click the pic for better quality)XHG7bZ4.jpg

At fully closed, the valve is still moving air through it. At fully open, the valve is still moving the same amount of air through it. Blocking the valve with my hand kills airflow to the engine and stalls it. Car is warmed up to temp and idling stable in the log. The only possible thing I can think of is the plumbing from the IAC to the ITBs isn't large enough to move enough air, but I seriously doubt this is it. Any ideas?

Edited by nmehdikh

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What size hose runs to the IAC?

550 rpm is really low for an L motor and really low for a large cam engine . You should be closer to 900 rpm.

Cold timing advance will help idle a lot .

Tuning warm up idle is not easy and factors in a lot of things . What timing are you running at idle , should be at least 15-17 degrees . You could set in about. 7 degrees advance at cold start up . 

You could try setting your idle adjustment for engine to idle with IAC clamped off when at tempature , then try and tune in a fast idle at warm up

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First, I suggest setting the itbs so that you can achieve a warm idle of say 900 rpm as mentioned, WITH IAC BLOCKED OFF. That way, you know the absolute lowest rpm you can achieve with the IAC.

 

Now unblock it. Try to incrementally increase duty cycle in 5% steps starting from zero. If the idle starts to drop towards 900, you are on the right track. Find the lowest point and make that your minimum DC. 

 

Edit: umm, basically, what madkaw said... 

Edited by bradyzq
Department of redundancy department

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I don't know anything about the bottom end of the engine, just that the block is stamped L26 and it has flat pistons. The head is a N42 that I only had rebuilt and got a Isky L-490 cam on, as well as new valve springs etc. Didn't do any head work. The header is a "Top end performance" 6-2-1, with mostly a straight section with followed by a relatively small magnaflow muffler.

Besides that its just the whole EFI / ITB setup. I'm honestly very surprised how much power it made, I was expecting 160-170ish.

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