Redtop Idle Surging - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Quiche2192 · 10-12-2022, 07:03 PM

The engine recently started surging and I am at a loss as to finding out what could be the cause. I have read around and tried diagnosing the following:

- The engine has been rebuilt and has been tuned and been running fine for months. IACV is new.

-Went to a drift event and at the end it started surging at idle. The engine starts normally then after a while it will start raising the idle to around 1700. Timing will then drop from 15 to 0, which causes the idle to drop. Then the cycle repeats.

-Checked vacuum leaks by using a propane torch and waving it around the intake. Hasn't pointed out anything.

-Replaced the O2 sensor, but hasn't made a difference

-MAF is OEM new

-Checked timing. It was at 20deg btdc. Turned the CAS almost all the way to get it to 15. Then the engine started idling normally again, but the it doesn't run right. Throttle is not very responsive. Plus if everything is good, 15 deg btdc should be when the CAS is centered. Mechanical timing is dead on.

-I'm thinking now that it might be CAS related.

So yeah I'm at a loss. I'd appreciate any input. Thanks!

Quiche2192 · 10-12-2022, 09:05 PM

Just went for a drive after verifying timing. Went fine in the beginning but got worse. At idle the car would rev to 4000 and stay there. So clutching in or going to neutral was not a good time. Timing stuck at around 39 when not giving any gas. Turned the car off and pulled the negative terminal from the batt. Put it back and started it again. Did the surge thing again where it would rev up to like 2000 and then back down and again up. I noticed timing fluctuating with the rpms again. So it looks timing related. Either CAS or even ECU. ECU is RSEnthalpy. Anyone have any experience with this?

Quiche2192 · 10-13-2022, 06:05 AM

So it looks like a high idle due to timing. Not due to air. I'm wondering why this is happening. Bad CAS, ECU, or wiring/grounding issue? Also the ECU is not throwing any codes

Quiche2192 · 10-17-2022, 05:00 AM

It ended up being the IACV. It just went bad

inopsey · 10-17-2022, 10:58 PM

did you replace or just clean the IACV?

*brndck* · 10-18-2022, 11:29 AM

Quote:

Originally Posted by Quiche2192

It ended up being the IACV. It just went bad

Quote:

Originally Posted by inopsey

did you replace or just clean the IACV?

yeah they get gunked up, esp if you have a turbo that is leaking oil past the seals.

i have never seen one straight up FAIL, but i have seen a number of them gummed up pretty good. normally i'll just soak em in purple power or carb cleaner, and then use a power probe to actuate it a number of times, then rinse and repeat.

10-12-2022, 07:03 PM	#1
Quiche2192 Join Date: Oct 2018 Location: FL Age: 33 Posts: 49 Trader Rating: (0) Feedback Score: 0 reviews	Redtop Idle Surging The engine recently started surging and I am at a loss as to finding out what could be the cause. I have read around and tried diagnosing the following: - The engine has been rebuilt and has been tuned and been running fine for months. IACV is new. -Went to a drift event and at the end it started surging at idle. The engine starts normally then after a while it will start raising the idle to around 1700. Timing will then drop from 15 to 0, which causes the idle to drop. Then the cycle repeats. -Checked vacuum leaks by using a propane torch and waving it around the intake. Hasn't pointed out anything. -Replaced the O2 sensor, but hasn't made a difference -MAF is OEM new -Checked timing. It was at 20deg btdc. Turned the CAS almost all the way to get it to 15. Then the engine started idling normally again, but the it doesn't run right. Throttle is not very responsive. Plus if everything is good, 15 deg btdc should be when the CAS is centered. Mechanical timing is dead on. -I'm thinking now that it might be CAS related. So yeah I'm at a loss. I'd appreciate any input. Thanks!

10-12-2022, 09:05 PM	#2
Quiche2192 Join Date: Oct 2018 Location: FL Age: 33 Posts: 49 Trader Rating: (0) Feedback Score: 0 reviews	Just went for a drive after verifying timing. Went fine in the beginning but got worse. At idle the car would rev to 4000 and stay there. So clutching in or going to neutral was not a good time. Timing stuck at around 39 when not giving any gas. Turned the car off and pulled the negative terminal from the batt. Put it back and started it again. Did the surge thing again where it would rev up to like 2000 and then back down and again up. I noticed timing fluctuating with the rpms again. So it looks timing related. Either CAS or even ECU. ECU is RSEnthalpy. Anyone have any experience with this?

10-13-2022, 06:05 AM	#3
Quiche2192 Join Date: Oct 2018 Location: FL Age: 33 Posts: 49 Trader Rating: (0) Feedback Score: 0 reviews	So it looks like a high idle due to timing. Not due to air. I'm wondering why this is happening. Bad CAS, ECU, or wiring/grounding issue? Also the ECU is not throwing any codes

10-17-2022, 05:00 AM	#4
Quiche2192 Join Date: Oct 2018 Location: FL Age: 33 Posts: 49 Trader Rating: (0) Feedback Score: 0 reviews	It ended up being the IACV. It just went bad

10-17-2022, 10:58 PM	#5
inopsey Nissanaholic! Join Date: Jul 2008 Location: canada Posts: 1,707 Trader Rating: (21) Feedback Score: 21 reviews	did you replace or just clean the IACV?