Rough idle and stall

[skyline084]

Hey guys,

I've checked the FSM and z32 sticky... still not figuring this out.

300 N/A

Car will run perfectly when cold but then when it warms up, the idle will become erratic and then die. If I leave a vacuum line off, it will idle high, but won't die. After the car is fully warmed, it won't even run at idle unless a vacuum is disconnected.

Compression is good, timing is good. Car will drive fine, just idle.

[nissanfreak12]

Check out the idle air control valve. Look it how to clean it and do not forget to reseal it to the plenum. You even may just need adjustment or even cleaning the connector.

It controls the the idle on our cars. The reason it doesn't cause issues when it is cold is because the there is another valve that is open which adds more air until it reaches operating temp.

[DCaff300ZX]

^^^^Correct, to me it sounds like you have a leak in one of the hoses in front or behind the unit, a common issue as they get abused moving things like the balance tube, spark plugs, injectors.
Also as mentioned, the IACV is "off" when cold started via another valve until warm and that valve closes putting the IACV in full control...and often causing a myriad of idle issues as it tries to stay on when it should not be, or is off due to a short/bad connection most likely due to corrosion or broken connector. Best fix if IACV still cleanable with WD-40/operational is an upgraded harness, if IACV still cranky (semi-common, happened to me) buy new and NOT used.
Another possibility if the above fails to fix the issue is the PTU harness that can be corroded at the connectors, and when the engine warms becomes more moveable and can cause intermittent idle issues. CTS and CAS connectors also have corrosion issues and worth a look/clean.
Good Luck!

[skyline084]

Thank you for the responses guys.. here is what I checked so far.

Connections are good going to every sensor. I do not know how to check for pulse when dealing with MAF and CAS. I have another CAS that I tried and still has same issues.
I also have another Igniter chip, changed and still have the same issue. I do not have a spare MAF, but the car stalls as soon as I unplug it.
I checked the ACC by applying 12v and it clicks on and off. I can clearly hear the idle change once plugged and unplugged.
Checked both o2 sensors through ecu and they both flash as should be when revving at 2k.
Hooked up a bike pump to MAF intake and pumped, did not hear any leaks. Also carefully sprayed carb cleaner around vacuum lines after the TB and did not hear anything.

I am kind of lost because I pulled the motor this winter and changed everything so it's hard to pin point. I deleted the aiv, egr and pcv systems. I also replaced both o2 sensors and installed new cats.
The car runs and idles perfectly at 1000-1200 rpms during cold starts, and as soon as it gets to operating temp and I begin to do some revs, it stumbles and surges up and down, then dies. The only way it will stay idling there after is if I leave a vacuum line, anywhere, unplugged.

Could this still be related to the IACV even though I hear the ACC click on and off and notice a change in idle once unplugged?

[nissanfreak12]

Have you checked the ECU for codes?

Have you tested the Coolant temp sensor? 2 wire sensor on the coolant tubes front of engine.

[skyline084]

Yes ecu doesn't throw any codes. Also checked the coolant sensor.. Replaced it during the rebuild

[nissanfreak12]

Did you replace it with a known "good" one? Or a new Oem or autoparts store one? I would still test it just to rule it out. You can always try and unplug it and see if that helps.

Also using a bike pump is not sufficient enough air movement to listen for air leaks, you need something with more volume. BUt chances are you may not have a vac leak because you get it to idle when you remove a vac line.

Another thought is maybe the IACV is set for too low of an idle. Try and loosen the idle screw out and see if that helps.

[skyline084]

When I disconnect the water temp sensor, the fans kick on and the idle raises, but will still surge once warm.

I will try to adjust the idle next, but not sure why this would change because I have never adjusted it.

I'm almost thinking the o2 sensors are just not working properly even though they flash consecutively. I've had issues on other cars where I've purchased Bosch o2 sensors and they just do not work properly.

[DCaff300ZX]

When I disconnect the water temp sensor, the fans kick on and the idle raises, but will still surge once warm.

I will try to adjust the idle next, but not sure why this would change because I have never adjusted it.

I'm almost thinking the o2 sensors are just not working properly even though they flash consecutively. I've had issues on other cars where I've purchased Bosch o2 sensors and they just do not work properly.

Agreed with the O2's, I've heard of bad ones often and of what you mention- they test "OK" but they get lazy and don't always function and cause intermittent fault codes.
I'd also mention that the IACV is a real PITA, on my TT the whole damn thing had to be replaced new ("good used" also was bad, advised this is always the case due to heat/crud buildup/age) as well as most importantly a new upgraded harness with moisture-sealed connectors and heat shielding.
Overall, most likely you need to remove corrosion and continuity from the possibilities with your sensors/electronics to get to the bottom of your issues...

[evildky]

O2 and CHTS both cause a rich condition which is fine for a cold start but can flood the engine once warm. If either of those is bad unplugging them will make no difference. You said you unplugged the chts, to be sure that's the one wiht 2 wire connector not the single wire.

[skyline084]

Thanks guys.. I got so fed up I just bought a perfectly running beater to swap parts... I swapped the maf, cas, igniter and iacv unit. Still having the stalling issues only when hot.. It will idle perfectly at 750 when warm but then when I get on it and come to a stop it will continue to surge from 250-1200 then stall. Going to swap out o2 sensors next, then tps, and last but not least, the ecu

[evildky]

If the issue only happens on decel but smoothes out after a minute it's the iacv.

[DCaff300ZX]

If the issue only happens on decel but smoothes out after a minute it's the iacv.

Yep, I gotta agree that frickin' POS IACV seems the culprit.

[skyline084]

It doesn't really smooth out, it just always happens at idle, only when it's hot. I replaced every sensor with good working ones... still had the issue. Left the car hooked up to battery overnight, come back out next day and I'm not getting fuel pressure. Swapped out pump with working one, still nothing. Ended up checking relays and everything was good but swapped out anyways. Swapped out ecu and car fires up.

The fuel pump makes a loud humming noise (It has since the rebuild and since this problem started) and only does it when I'm off the accelerator. The fuel pressure is still good, and so is the pump.

Okay, now to go back to the beginning. The power steering reservoir cracked on the bottom and leaked fluid into the alternator. This caused the regulator to crap out, which resulted in 19V going everywhere. I didn't notice this until it shorted out the fuel control module. I'm pretty sure that the 19v just destroyed every sensor. I think the car is cursed.

[z.Leinbach]

have you tryed a NEW TPS?

[skyline084]

Not yet . I will tmrw. Just wondering if you guys possibly have any insight on why the fuel pump would be making this whine noise.. It didn't do it on the car I just pulled. It only whines when I'm not on the throttle

[RubyRed300ZX]

300 N/A has a fuel pump control module behind the driver's seat. Allows for two speeds (3 on a TT). The whine might be because it's still on high speed at Idle when it should not be. Or, the pump itself is ready to fail. Over engineering at its finest.

[skyline084]

I agree completely. I changed that already. I interchanged so many parts because I have another 300 so I'm just swapping back and forth. Something must be very messed up within the wiring.

The fuel pump will not prime now. I swapped out ecu, pumps, fuel pump control modules, and relays. It still won't prime! lol.

[DCaff300ZX]

Not too sure about the fpcm whine, mine has done this since my engine work as well and a new pump and Doug's intervention has found no cause, solution, or problem other than the whine is less noticeable since a complete fuel line clamp tighten pass I did. Personally I have wondered about my very large injectors used in my upgrade work, but since then have seen so many others complaining of the fp whine I've realized it isn't specific to me and my car. I am currently finally getting to my PTU harness replacement and recirc hose replacement this week, hoping but doubting that helps anything but I can alway wish.

Back to your problem, with you now having no fuel pump prime are you still so sure the pump is good? Can you swap in a known good/working unit?

[skyline084]

I could see larger injectors causing a whine but not really lol. Yup, I have two z's so I've been swapping back and forth parts

[skyline084]

Okay, so I have finished swapping parts back and forth between the working and non idling Z. The problem persists even with all the working parts currently on the car. The AIV and PRVR solenoids would not have anything to do with a hunting idle would it?

I feel like this is an IACV problem, but I put a working one on and it is still there. Once the car is warmed up and the Air regulator valve shuts, the idle begins to hunt between 250-1250 or so, then stalls.

Next thing I am going to check is the entire EFI harness and ensure that everything going to the ecu is receiving the right voltages and has continuity between each sensor and the ecu. Or just swap harnesses and call it a day.

[DCaff300ZX]

BTW, turns out my PTU harness replacement DID stop the fp whine, and also my cold idle issues and throttle response are perfect finally.
I've had the harness for many months, and now kick myself for taking so long to replace it...may well be your issue as well. I have worked over the old harness three times and each time it would solve my current problem, but would always come back eventually or sooner.
Hope this helps!

[skyline084]

Good to hear man! Glad to see someone got a chance to see the light at the end of the tunnel! lol

I think my issue is related to the fuel circuit. The pump stopped working a few days ago out of the blue.. It was whining very loud before that happened. Now, after grounding the plug out on the back, bypassing the fuel pump control module, the pump is quite again and fuel pressure has returned. Maybe bad grounds in the circuit?

[skyline084]

DCaff, did you take a look at the ptu harness while you were having those symptoms? Did you check to ensure that you were getting the correct voltages and continuity existed between each wire?

[DCaff300ZX]

No, I didn't actually and had bought the PTU harness simply as an insurance since I had assumed I had it cleaned and working to spec. It WAS clean when inspected upon removal and nothing out of line, but I also had long suspected the harness simply because of it's excessive size and previous location in the worst place possible for it- the front of the engine.

Anyway, upon driving the car I find it has solved several small issues such as slight surging and the annoyingly poor throttle response until 83 degrees + celsius, but has now also LOWERED the operating temp of the motor further to about 81C (80F+ degree day today, 1 hour driving) and the engine still doesn't respond as well as it does when and if I can get it to 83C and higher...about 5 minutes at the end of my drive after sitting in some traffic finally. I am completely stumped at having a high HP tuned TT that runs cold on OEM cooling system (OK, new CSF rad in OEM size/config) and why/how that can be affecting performance through my tuned setup...

[skyline084]

What kind of setup are you running (turbos, ecu, injectors)? Did you replace the PTU along with the harness? Sounds like you're still having issues though huh?

As for my problem, I replaced every sensor from my working Z onto this pos.. I am going to get some piping to pressure test my vacuum for leaks. I visually inspected everything and replaced all vacuum lines, so not sure what I'm going to find. I deleted most of my vacuum so there really isn't much to check. I can get the car to not idle hunt if I unplug the air regulator so it stays open. That little extra amount of air allows it to idle smoothly. Almost ready to just swap in a TT