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Discussion Starter #1 (Edited)
I recently had to remove the intake on my GTR to reseal the coolant bypass tube on the bottom. I'm a ceritifed nissan tech in canada so i'm not ignorant to fixing cars.... just my skyline... lol. While it was apart I thought i'd clean the butterflies, they were carboned up pretty badly. after reassembling the intake and the car it Idled at 1100-1200 when cold, then as it warms up the idle goes up to 1600 rpm. I thought it was a simple vaccuum leak. I took a smoke machine and pressurized the entire intake with smoke, no leaks anywhere. I used a consult scan tool to monitor the readings and everything seems to be fine, TPS is good, aac is ay 2 % and if i go in to manualy open it the idle does increase. the only thing i can see is that the alpha is at 80%,. Which seems far too lean. I removed the intake once again to double and triple check everything. The only thing i can fugure is that either the air regulator is faulty or I read a post where it was said the butterflies have a special sealant on them... I've checked the throttle linkage to make sure the butterflies are actually closed. i have the whole assembly laying on my work bench and to look at them they look perfect, all adjustments and the position of the butterflies inside the chambers are good. Any help or suggestions would be greatl appreciated!!!
 

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Would it not just need time for the ECU to reset itself and set the idle again?

It may be letting slightly more air in now you have cleaned the butterflys when they are closed?
 

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IIRC the throttle plates actually have some material on them from the factory to help them seal properly when they close. If you've been a vit vigorous when cleaning you might've removed this and the plates aren't closing properly. Like you said - already covered in a previous thread.

There was a thread on here a while ago about pressurising the intake system - i.e. remove the intake up to the turbos, cap off the turbo intakes and thread an air connector in to allow you to attach an air pump. Make sure you have a pressure gauge hooked up so you can see the pressure in the intake system. I'm thinking that you could then remove one spark plug at a time - if there's no pressure drop then refit the plug, and onto the next. This way (I'm thinking) if your throttle butterflies are leaking (i.e. aren't shut properly) then you'll see the pressure drop when you remove the sparkplug from the cylinder with the leaking throttle butterfly. Of course, if the piston's TDC or close too it and covering the intake it kinda makes it difficult!

Just MHO anyway :)
 

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I recently had to remove the intake on my GTR to reseal the coolant bypass tube on the bottom. I'm a ceritifed nissan tech in canada so i'm not ignorant to fixing cars.... just my skyline... lol. While it was apart I thought i'd clean the butterflies, they were carboned up pretty badly. after reassembling the intake and the car it Idled at 1100-1200 when cold, then as it warms up the idle goes up to 1600 rpm. I thought it was a simple vaccuum leak. I took a smoke machine and pressurized the entire intake with smoke, no leaks anywhere. I used a consult scan tool to monitor the readings and everything seems to be fine, TPS is good, aac is ay 2 % and if i go in to manualy open it the idle does increase. the only thing i can see is that the alpha is at 80%,. Which seems far too lean. I removed the intake once again to double and triple check everything. The only thing i can fugure is that either the air regulator is faulty or I read a post where it was said the butterflies have a special sealant on them... I've checked the throttle linkage to make sure the butterflies are actually closed. i have the whole assembly laying on my work bench and to look at them they look perfect, all adjustments and the position of the butterflies inside the chambers are good. Any help or suggestions would be greatl appreciated!!!

I made this same mistake of cleaning the throttle bodies...............idle 1600-1800rpm, bought a new set. I have not fitted them yet, but was advised that this was the problem as air is now managing to pass the closed butterfly.

That will teach me :chuckle:

Cheers
Ian
 

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strange i sandblasted mine without issue..

the throttles are supposed to be slightly open too...well going by the workshop manual anyway
 

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Mine does this and the throttle bodies were not touched.

Butterflys would come set at a position as "closed" from the factory but I would doubt if they were truely fully closed as I remember reading in an Auto-engineering book that they are set very slightly open. It could be that the closed position is a bit out from factory one now although that didn't appear to be the problem with mine :( - mine is currently with Robbie at Trackday Performance getting the high idle looked at - here's hoping - I'll let you know how it works outs.
 

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I took a smoke machine and pressurized the entire intake with smoke, no leaks anywhere. chambers are good. Any help or suggestions would be greatl appreciated!!!
How do you hold pressure in all of the cylinders to check the intake system? one of the exhaust valves will be open.I would say a air leak, or the Air Bi pass valve is fully open.
 

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How do you hold pressure in all of the cylinders to check the intake system? one of the exhaust valves will be open.I would say a air leak, or the Air Bi pass valve is fully open.
So long as you're not in an overlap period on the cam I would've thought that if the intake valve's open then the exhaust will be closed...?
 

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The cylinders will be at a different part of the cycle so One will have its valves open.
I noticed my idle rised when I removed my AC pump.I wonder if it needs a resistor put across the plug to stop the ECU thinking its engaged and driving the Bi Pass valve.
 

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I recently had to remove the intake on my GTR to reseal the coolant bypass tube on the bottom. I'm a ceritifed nissan tech in canada so i'm not ignorant to fixing cars.... just my skyline... lol. While it was apart I thought i'd clean the butterflies, they were carboned up pretty badly. after reassembling the intake and the car it Idled at 1100-1200 when cold, then as it warms up the idle goes up to 1600 rpm. I thought it was a simple vaccuum leak. I took a smoke machine and pressurized the entire intake with smoke, no leaks anywhere. I used a consult scan tool to monitor the readings and everything seems to be fine, TPS is good, aac is ay 2 % and if i go in to manualy open it the idle does increase. the only thing i can see is that the alpha is at 80%,. Which seems far too lean. I removed the intake once again to double and triple check everything. The only thing i can fugure is that either the air regulator is faulty or I read a post where it was said the butterflies have a special sealant on them... I've checked the throttle linkage to make sure the butterflies are actually closed. i have the whole assembly laying on my work bench and to look at them they look perfect, all adjustments and the position of the butterflies inside the chambers are good. Any help or suggestions would be greatl appreciated!!!
Have you found the problem yet?
 
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