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Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars


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Old 11-27-2019, 06:10 PM   #1
Dan90240
 
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Unhappy S13 Ka24de idling at 1500

So I bought a 1990 s13 with a dohc swap and when I got it the little hose next to the bigger iavc was disconnected and plugged. It was idling right where it was supposed to, but would drop a little when I pressed on the brakes, which were very soft due to a leak in one of the hoses. After I reconnected that vacuum line the idle went up to 1500-2000 but no longer bogged when I braked. I replaced the front brake lines and after I bled the brakes the pedal got super stiff. I sprayed throttle body cleaner around most of the vacuum lines and the brake booster vacuum line but didnt notice any real change in the engines idle speed. It did go down for a second at some points when I was spraying (around the tps and egr) but I couldnt re create the effect. I tried adjusting the iavc idle screw but couldn't get it to drop past 1500. Could it be that it's just a bad brake booster? Is replugging the little hose on the intake a good idea? Any help is appreciated I am new to ka engines
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Old 11-27-2019, 08:44 PM   #2
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Vacuum leak or idle air control valve
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Old 11-28-2019, 06:50 PM   #3
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I'd check hoses for cracking. When I got my S14 it had like 5 vacuum leaks and was idling at a cool 3500 lol. It had been garaged for like 7 years cause he couldn't pass emissions and gave up.

There is a vacuum for the EGR on the back of the valve cover, in my case it had no hose at all because they deleted the EGR and didn't realize it was a vacuum line I guess, but it's worth checking it for cracks. Make sure none of the tubes are kinked. I would also put the IACV back where it was.

Another thing is the IACV gets gummed up after awhile. Spraying carb cleaner into the vac tube that runs under the intake manifold can help clear it out, but that will kill your engine so you have to do small spurts and rev the throttle a bit to keep it alive.

If you can gain access to a smoker, that would be the easiest way to find your leak.

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Old 12-02-2019, 02:18 PM   #4
kyral
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what do you mean by little hose next to the big IACV?
theres a couple hoses near the IACV and a little one sounds like FPR hose.
please clarify

also if you acutally have no vacuum leaks. a simple adjusting of your TPS and iacv can very easily drop your idle back down if you have no other issues
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