300zx na will not hold idle

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Slickrick052000
Posts: 4
Joined: Sun Jul 19, 2020 4:11 pm
Car: 1991 Nissan 300ZX NA

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Hey All,
Have a 1991 300zx na that starts and revs fine but will not stay on and if it does it is at a very low RPM say 400 or so and then it will eventually bog down and die. We have tried replacing the mass air flow sensor, TPS(Adjusted to spec) and nothing has improved. We have also tried to adjust the idle by the idle air control valve and there is little to no change which is concerning. Why is it at least not responsive to that? A massive vacuum leak maybe? We have searched and searched visually and tried to hear a leak and can’t seem to locate it if there is one. Has anyone experienced this or have any suspicions on what the culprit might be? Any advice would be appreciated. Thx


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AZhitman
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Welcome aboard!

Don't mess with the IACV. Have you put an OBD scanner on it?

A vac leak is likely, but there's a possibility of fuel pressure issues as well. Fuel filter?

Vac leak won't be audible, use starting fluid or a smoke machine to find leak. Z32 engine bay is a cluttered mess, so to think you'll easily see or hear a vac leak is... well, funny. ;)

Slickrick052000
Posts: 4
Joined: Sun Jul 19, 2020 4:11 pm
Car: 1991 Nissan 300ZX NA

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No I have not hooked up an OBD reader to it or tried the smoke thing but my bro just suggested that. Will give it a try. We did change the fuel filter. Let me see about testing the fuel pressure.

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NolimitZ32
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Car: 91 AG2 2+0 TTMT swap/E39 BMW 540i6/E53 4.6is Dinan S3
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The symptoms you describe could be a combination of the TPS and CAS adjustments being off. Also you said you adjusted the TPS but have you confirmed its good? These sensors have a tendency when well used to develop flat spots that give inconsistent voltage readings.

Slickrick052000
Posts: 4
Joined: Sun Jul 19, 2020 4:11 pm
Car: 1991 Nissan 300ZX NA

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The tps is new and yes I believe we adjusted it accordingly with a multimeter per this forum. However, I have not considered the CAS. Will put that on the list. I’m currently waiting for my vacuum leak detector to arrive. Thanks

Slickrick052000
Posts: 4
Joined: Sun Jul 19, 2020 4:11 pm
Car: 1991 Nissan 300ZX NA

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Update...I got around to using a smoke machine to test for vacuum leaks and a pretty big leak emerged from the lower intake tube on the driver side. I hope this is my problem but we shall see. Gonna get down there over the weekend and see what I’m dealing with.

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sns00
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Car: 1994 Z32 TT
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