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Old 04-04-2017, 02:07 PM   #1
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Popping At Idle

Hi all! I've never posted on the forum before, so this'll be a first.
I'm also not the most experienced with engine work or familiar with names/specifications.
Anyway, I've got a 1993 Nissan 240sx Coupe with a KA24DE in it. It's naturally aspirated and the only things ever done to it were belt changes and fluid changes as well as a new fuel pressure regulator.
The problem that has just recently developed is a rough idle. I have no clue what it could be other than maybe the MAF (that's I've read), the Valve Cover Breather, or maybe the Timing/Distributor. I'm not sure how to check each thing or even if those are what is causing the issue.
When I start the car up, it idles fine around 700 (which is what it usually idled at before the problem so it's fine), but when I give it a little bit of gas, it comes back down and settles at 1400-ish RPM and I can just hear a continuous popping sound coming from the exhaust. The clutch also feels a bit stiffer now too.
My main concern is the popping and it only does it when the car comes to rest at an idle. The popping is pretty consistent, but I just don't know what it could be. Any help with explanations is greatly appreciated!
Thank You!
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Old 04-04-2017, 06:22 PM   #2
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It's a misfire or detonation. Either NOT good...
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Old 04-04-2017, 07:10 PM   #3
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Originally Posted by S14kouki805 View Post
It's a misfire or detonation. Either NOT good...
How would I determine what it is? And what could be the cause of them?
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Old 04-04-2017, 08:31 PM   #4
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Not sure exactly, could be the timing, if you don't know what you're doing take it to a mechanic
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Old 04-10-2017, 08:11 PM   #5
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Unplug your injectors one at a time and try to isolate the cylinder that is causing the issue.

You are not giving us much to go on. My best guess is a leaking injector or misfiring due to plugs/wires/distributor cap.
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Old 04-11-2017, 05:28 AM   #6
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Originally Posted by p00t View Post
Unplug your injectors one at a time and try to isolate the cylinder that is causing the issue.

You are not giving us much to go on. My best guess is a leaking injector or misfiring due to plugs/wires/distributor cap.
Well what else could I tell you about that would give your more information or a better idea of what is going on? And yeah I'll see if that works.
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Old 04-21-2017, 05:19 PM   #7
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remove the fuel rail with the lines and injectors still on it. have your buddy turn the key on and you'll hear the fuel pump prime the lines for about 5-10 seconds then turn the key back off and repeat a few times. while hes doing this, see if fuel is leaking past one of your injectors. you may need oring replacement on one of them
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Old 04-21-2017, 09:37 PM   #8
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You said it settles at 1400. That is a high idle. The popping is probably a lean condition brought on by the high idle. High idle is caused by too much airflow.

You have an air leak somewhere. I would block the IACV channel, the hose that leads to the IACV, with a vice grip, and see if that brings down the high idle. If it does, replace or clean the IACV.

otherwise, there is an air leak somewhere else. Look for broken hoses. If you can't find the leak visually, try soapy water. If that doesn't work, then do a pressure test. Google "boost leak test", basically use a compressor to fill the plumbing with air, to find leaks.

Leaking air (air leaks) cause high idle conditions. Idle is controlled by airflow, not fuel, not spark.
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