Misfiring, losing throttle, violently shaking at 3,500 RPM's when cold

1993 NISSAN SKYLINE
53,000 MILES • 2.0L • 6 CYL • TURBO • 2WD • MANUAL
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MTHUDE
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Hi, I actually drive a rb20det swapped s13 to clear things up.

My rb20det is sucky when it's cold started, and it runs completely smooth when it has warmed up a little. When it's cold it idles super low, i can't rev above 3,500 RPM's without it popping or misfiring constantly and i can't go over RPM's in neutral. When i do that in gear it does the same thing but it violently shakes the car back and forth.

I have changed the coil packs to splitfire’s, i have changed the spark plugs more than enough times, my MAF is new and clean, my grounds are good, and i am having no vacuum leaks to my knowledge. The only thing i don't have is an IACV-AAC, seems the previous owner disconnected it or broke it somehow so i have one ordered. i wonder if it will fix my problem. Any help is welcome thanks.
Nov 15, 2020 at 2:14 PM
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JACOBANDNICKOLAS
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  • 110,175 POSTS
Hi,

The idle air control valve is responsible for maintaining engine idle speed. I don't know if it is related. Do you have a live data scan tool? If you do, check two things for me. When it is cold, check what the coolant temp sensor signal is sending to confirm it is close to the actual temperature. Also, let me know what the short term fuel trims are.

If you do have a scan tool, are there any codes present? Also, most times a popping or backfire is caused by a rich fuel mixture. The ECT and fuel trims may indicate an issue. That's why I asked. If there are codes, let me know what they are as well.

Here is a link that explains how to fix a backfiring issue. I don't know if it is relevant, but there could be something that you may find of interest.

https://www.2carpros.com/articles/engine-backfires-while-running

Let me know. Also, let me know if you have checked the fuel pump pressure.

Take care,
Joe
Nov 15, 2020 at 5:31 PM
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MTHUDE
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I have an obd1 not and obd2 so i don't know if i can use a data scanner to spit codes at me. if I can i will check tomorrow and update you. Thanks :)
Nov 16, 2020 at 12:07 AM
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JACOBANDNICKOLAS
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Hi,

Sorry about that. I see OBD2 so often, I simply missed it. Here are directions for getting OBD1 codes from a Nissan. I don't know if you already did this, but I thought it may be helpful.

https://www.2carpros.com/articles/nissan-obd1-diagnostic-trouble-codes-and-retrieval-procedure-1984-to-1994

Let me know.

Joe
Nov 16, 2020 at 4:01 PM