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you probably wont get any help here with out more info. Does it happen when driving, for example you are driving put it in neutral and it does this?
I saw you checked codes and o2.
I would guess a vacuum leak, check for leaks and make sure it is all correct..

http://www.twinturbo.net/nissan/300zx/forums/technical/view/1089590/Mostly-Complete-Vacuum-Diagram.html

Could also be TPS or IAC (IAA, did you adjust this when you replaced it?), but i really dont know..

http://www.twinturbo.net/nissan/300zx/tech/iaa/iaa.html

hope that helps?
Matt
 

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Discussion Starter #3
This actually happens at cruising and idle. If I'm maintaining speed it's like the engine just loses power suddenly and I've only tried pumping the gas pedal a few times so not sure if that helps but after 5 or 10 seconds it recovers. It can happen once, a couple of times, or not at all on the freeway. It also happens at idle but it seems rarer. As of the problem starting roughly 2 weeks ago and all the driving I've done, it happening at idle has happened maybe 3 or 4 times. When it does happen, it stalls out. I'm guessing that it doesn't die on the freeway is because it's in gear and the forward motion keeps the engine running. Since this problem has happened, I verified that the TPS and IAA are set spot on. When I get some more daylight tomorrow, I'm going to verify that the MAF is actually working correctly. If the MAF is actually not working, I'll be peeved as I bought MAF cleaner before all this and cleaned it carefully as per online and bottle instructions. I did check the vacuum recently also. It metered at 19-21 and it was bouncing back and forth. That is indicative of a leaky valve seal but it has had that symptom for the last 5 months and ran fine.
 

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Mine bounces between 18-19psi and I don't have that problem, keep looking.

Codes gave an all clear?

Have you check over all your connectors for green death?

PTU especially?
 

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Discussion Starter #5
Codes were all clear and over the last few weeks I have inspected 90% of all connectors including the PTU and MAF connectors. What corrosion I found, I cleaned and even replaced the PTU. I did however check the diagnosis in the online Field Service Manual and unplugged the weak driver's side O2 sensor according to the unstable idle troubleshooting process and my idle seems solid now. Also, no stalling with the limited testing I've done....
 

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Discussion Starter #6
OK I'm still having the stalling problem but otherwise, my idle is rock solid. I have to replace the O2 sensor for sure and I'm going to order a consult adapter tonight. I hope it helps.
 

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you know the same thing was happening to me it was MAF sensor i spent a lot of money before i fond out what it was. if you have a friend that has a 300zx ask him if you can swap out the MAF sensor before you buy one if thats it you know what to buy if not you didnt wast any money
 

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Discussion Starter #8
Ya good idea. Now I just need to make a friend in the California Bay Area that owns one of these. I think there are like 5 in my county LOL
 

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Discussion Starter #10
I'm in Contra Costa. You? Small update: I removed the plenum cover and stuck a screw driver on each injector. all were ticking but while I was checking one, I put the screwdriver on it and started to lean over and listen, the engine just... stopped... no putting, no choking, just stopped. It re-started right away and I checked the rest of the injectors. I'm starting to think this is electrical. Before that, I took a short drive after it not stalling all day on me, and it started to loose power while driving. pumping the gas didnt help so I decided to experiment and pull it out of gear. It stalled immediately. Whatever is the problem, it seems to be getting worse. Just for the record, I've tested the following;

IAA (Replaced)
Fuel Filter (Replaced)
Fuel Pressure Regulator (Replaced)
MAF (Tested)
Injectors (Tested)
Power Balance (Tested)
Vacuum (Tested with gauge and via pcv hose pinch test)
TPS (tested and set)
Fuel Pump Relay (Replaced)
Ignitions Coils (Tested)
Knock Sensor (Replaced and Relocated)
Passenger O2 Sensor (Tested)
Driver O2 Sensor (BAD! Awaiting Replacement but running with unplugged)
Alternator (Replaced)
Thermostat (Replaced)
Radiator (Replaced)
EGR Solenoid (Replaced)
PTU (Replaced)
CAS (Tested)
Multiple Connections Cleaned and grease applied
 

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Discussion Starter #11
Another note: This problem seems to be very intermittent. I can drive around for a bit and it might not happen. On the other hand, Sometimes I just have to drive down the block. The more I lay on the gas, the sooner it happens it seems. Some other interesting things that may be related; When I turn on the headlights, The RPM drops maybe 200rpm. I just replaced the alternator a month or two ago but it went bad in traffic and I drove it all the way home. The battery went dead and sat for a day. Then I put in the new alternator and it started right up. both have been fine ever since it seems.
 

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Discussion Starter #12
Oh and another thing, as of recently, sometimes, when someone gets out of the car, they may get a bit of a shock on the door. Not a huge one though. I attributed it to clothing rubbing on the leather seats...
 

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Discussion Starter #13
I'm thinking about my next step. I can either get a new O2 sensor+consult connector or a fuel pressure tester. Which would you get?
 

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My .02: Fix what you know is bad and then proceed from there.
 

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Discussion Starter #15
I agree. I'm thinking it would be worth getting my battery checked for free but the malfunctioning (or unplugged) O2 sensor may be masking or causing systems that confuse the diagnosis.
 

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Do what Cuiz-Z said and then proceed. You can't analyze when you know you have some parts not working correctly.
 

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Discussion Starter #19
OK important update:

I drove my friend to the store today. The Z stalled and would not restart. I don't know why but I asked him to stomp on the floor where the computer is located... The car restarted.. I think I found my intermittent issue... There is a Ashspec computer installed but the PO gave me the factory computer when I bought the car. going to re-install factory computer tomorrow, test drive and re-update again. Before anyone asks, I checked the ECU harness and it was immaculate and completely connected today. I checked it 100% today. Further details inc. and also a new O2 sensor.
 

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Discussion Starter #20
Fresh new day and I got into the computer area today while the car was running and tapped every box, wiggled every wire. No stall. I'm back to square one. I should be getting what I need today in order to easily replace the driver's side O2 sensor. After that, we'll see how things go.
 
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