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Old 01-08-2014, 11:06 PM   #1
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vaccum leak / high idle rb26

Finally got my rb26 swapped rx7 dynoed and tuned . MAde 525 whp. I keep blowing off vacuum lines . i found alot of them and capped them off . My idle is 1500 rpms and will go higher when warm. tried spraying carb cleaner to find more leaks with no luck . what are the most common leaks ? i dont think its the IAC because under boost im misfiring now . ran great on the dyno . Any help would be great
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Old 04-08-2014, 12:07 AM   #2
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There's a couple bad ones near the rear turbo (assuming you're on the TT set up still)

There's a stickler under the "twin turbo" pipe that connects to the soft(er) line too.
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Old 04-08-2014, 02:12 AM   #3
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Running a 6765 single turbo . car is tuned professionally . sometimes it pulls hard and sometimes it cuts out under boost. Idle is 1500 and creeps to 2000 when warm !
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Old 04-08-2014, 07:55 PM   #4
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Hoepfully all works out well…that would be tough to diagnose without looking at it. I could be more useful if you had a stock set up. A lot of variables now that I know it's a single turbo.
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Old 19-09-2015, 03:44 PM   #5
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Hoepfully all works out well…that would be tough to diagnose without looking at it. I could be more useful if you had a stock set up. A lot of variables now that I know it's a single turbo.
Don't mean to hijack the thread, but I have a somewhat similar problem on a bone stock RB26TT setup, 98,000 kms original. Here is my situation.

When I first got the car about a week ago, car idled around 800 RPM when at temp. Seemed a little high but didn't think much of it. When I was followed by my wife in her car, she said when I would throttle it and get boost that I would have some dark smoke (assuming black) poof out.

Then last weekend I started the car cold and blipped the throttle a couple times up to about 3k (stupid, I know) and ever since the idle sits at 1500 rpm when cold, and rises when at temp to about 1800 - 1900 rpm. Still seems to hold boost fine and no other issues. No misfires, idles very very smooth, just high.

I cleaned the AAC valvle and installed a new gasket with it. Not fixed. I'm about to go hunting for vacuum leaks, but am wondering if there are specific areas I should check so I'm not just spraying carb cleaner everywhere.

Any help appreciated!
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Old 19-09-2015, 05:27 PM   #6
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Just went over the motor with carb cleaner in the areas I would expect a vac leak. Nothing interesting, just consistent high idle.
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Old 19-09-2015, 06:03 PM   #7
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Have you guys checked the cold stat valve, if failed it could be open and be letting too much air in, its still under the plenum on the RB26 I think.
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Old 20-09-2015, 09:34 PM   #8
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Have you guys checked the cold stat valve, if failed it could be open and be letting too much air in, its still under the plenum on the RB26 I think.
That is next. Its just such a pain to get to. I'm thinking about diagnosing it by pulling and plugging one end of the IACV line at the plenum. Is that a bad idea for any reason? I'm thinking if I just pull the hose and plug it that at least I would effectively be bypassing the valve and hope to see my idle drop. Ambient temp is obviously not cold right now so I don't think it should be a problem.

See attached image for where I'm thinking about pulling and plugging. I circled the connection in blue. Ignore the red arrow.
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Old 21-09-2015, 08:56 PM   #9
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What about cleaning the MAF? If that's gunked up, you could be getting bad O2 readings from the start.
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Old 22-09-2015, 03:39 AM   #10
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Fixed

Fixed! MAF could have made sense too but it was the Air Regulator. Seems stupid that these can fail open. Should be designed to fail closed.

Anyway I made up a little bypass kit that didn't require me to remove my plenum which sounded like a big PITA.

See attached for my simple kit, 2 hose clamps and an additional 19/32" hose segment which is close enough in size to the 14mm. You could also just split the stock hose, but that was too much work. Took 5 minutes to install. I 3D printed the hose plug fitting at home. If anyone ever wants one, feel free to PM me and I can send you the file to have it printed. Alternatively you could probably just use a bolt and a vacuum cap.
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Last edited by chambers; 22-09-2015 at 03:50 AM. Reason: change hose size
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Old 30-09-2015, 10:46 AM   #11
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Missed this, glad its now sorted, if I had caught it earlier I could have saved you the trouble of making the plug, as all you need to do to diagnose the cold start valve is pinch the rubber pipe where it enters the plenum with a pair of long nosed pliers and see if the revs drop...sorry.
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