# z31 mysterious sputter



## eishiba (Sep 23, 2009)

I have an 85 300zx 5 speed turbo. When I start this car, it will run for about 2 minutes fine for the most part. Then it starts to act as if its not getting any gas and sputters REALLY bad. It will die if you dont give it any gas. The tach has gone down as low as 300rpm trying to stay running when I'm giving it gas so it doesn't die. After another 2 minutes, it stops and the cars power returns and runs just fine. You can drive it for hours after that and it runs fine. Its just those first few minutes that is has this problem. Once the sputter has stopped and it runs fine, you can turn it off, turn it back on, and its still fine. This sputter will happen again if you leave the car off for maybe an hour or so. I have changed the tps sensor, crank angle sensor, and the fuel filter. I thought if the fuel pump was bad, then you could simply NOT hear it run when you turned the car to the "on" position. I have two videos below. One outside the car, and one while driving.

https://www.youtube.com/watch?v=O-AHlzTp1kg&list=UUJQZa8n-f8KP7hrC7SvcQGg

https://www.youtube.com/watch?v=J_66e4RkVm4


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## rogoman (Dec 16, 2004)

With the engine cold, does the sputtering occur only during idling or does it also occur when driving at highway speeds? Have you done a full tuneup? Perform an ECU code readout for any possible fault codes that may be set.

When the engine is cold, the idle speed should be around 1200 rpm, then after a few minutes the speed should drop down to 650. If you don't have the fast idle with a cold engine, then the air regulator may be bad.


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## eishiba (Sep 23, 2009)

rogoman said:


> With the engine cold, does the sputtering occur only during idling or does it also occur when driving at highway speeds? Have you done a full tuneup? Perform an ECU code readout for any possible fault codes that may be set.
> 
> When the engine is cold, the idle speed should be around 1200 rpm, then after a few minutes the speed should drop down to 650. If you don't have the fast idle with a cold engine, then the air regulator may be bad.


This occurs whether you are driving or just sitting in your driveway. It seems to be timed somehow. And I have error codes for it.


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## rogoman (Dec 16, 2004)

What are the error codes?


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## eishiba (Sep 23, 2009)

rogoman said:


> What are the error codes?


The only error code it has is for the clutch neutral safety switch since the car is a 5 speed and can start without pushing the clutch in. Thats the only error it has but I doubt that is it.


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## eishiba (Sep 23, 2009)

Ok, I am updating because I decided to take it to a shop. I'm going to type everything that they did and said in the report. 



Test drove. During warm up, started running bad and hesitated. Only ran bad for a few minutes then ran ok. Checked codes. Has a code 12 for MAF problem. Tested MAF and passed in ALL DATA. I even checked input at the ecm. It matches the reading at the MAF.

Test Drove and coolant sensor input at ECM did not drop out or jump at too (I can't tell what they wrote here. I could be mistaken but I think it says "too cold or too hot") input when it acted up.

Scoped ignition system. All looks normal. Check ignition timing at 20 degrees BTDC. Spark plug #3 was loose. Tightened to torque specs.

There is a rattling, squeaking noise from behind the timing belt cover. Sounds like a bearing trying to lock up. If timing belt jumps on this engine it will bend the valves.

Test drove while monitoring MAF input at (I want to say it says ecm but it looks like pcm). The input did not drop out when car acted up. So I think the MAF is ok.

Checked fuel pressure. Has 30 psi with vacuum to regulator. 40psi with no vacuum. Has 30 psi when shut off. Spec is 30 psi and 37 psi. Fuel pressure is not the problem.

Every time my hand is near the distributor cap I get shocked. Found there is a secondary leakage out the cap around the #2 plug wire connection area. Needs a new cap but probably won't fix the problem. 

I give up. I don't know whats wrong with this vehicle!



I found it funny that a certified auto mechanic put that last part in the report. I'm going to change the distributor cap tonight. Any other ideas?


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## BeyondBiscuits2 (Jan 18, 2006)

from your posts, I gather this only occurs when the vehicle is cold (i.e. not warmed-up), and at low rpms. Have you considered checking the intake manifold gaskets, both upper and lower? A bad intake manifold gasket will cause all sorts of hesitation and suttering when cold and at idle that magically disappear at driving conditions. Also, the VG30 (in any variety) is known to be a carbon monster. My engine used to stutter and sputter at start up for an extended few minutes until it warmed up, and then it would run just fine. This issue was caused by carbon buildup, which was fixed when I rebuilt my engine (I did not re-ring the pistons, by the way). I fixed it by having my intake manifold and cylinder heads chemical dipped, but you might try something as simple as Seafoam. Just my .02.

Also, I just recalled this. I worked on a '85 Turbo that was being prepped to be sold. The car would run fine for about 5-10 mins, then just die. You could keep it alive by feathering the throttle. We ended up, in a bit of desperation, replacing the ECU with one from an '85 NA. It cured the problem. Once we replaced it with a proper Turbo ECU, the car ran like a champ and never gave us any other problems.


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## CMax03 (Jan 17, 2009)

Spray some WD40 inside your capand see if it clears the problem...A cracked cap is cheap and can cause a nightmare like what you're having....I would also inspect and clean all my engine harness grounds!


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## rogoman (Dec 16, 2004)

eishiba said:


> There is a rattling, squeaking noise from behind the timing belt cover. Sounds like a bearing trying to lock up. If timing belt jumps on this engine it will bend the valves.


If the rattling/squeaking sound is really inside the timing belt cover, then the belt tensioner may be ready to fail. Also the timing belt needs to be replaced every 60,000 MI. If I was you, I'd tend to that as a top priority.


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