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Discussion Starter #1
1987 Turbo - K&N Intake, custom exhaust, boost set at 9.5psi, 91 octane fuel (it goes pretty good).

The engine starts hard when it is totally cold.
It will fire, then seems to sputter on one or two cylinders and then it will catch and run fine. It has always started.
The fast idle works fine.
Once it warms up, it idles at about 750 rpm but will stutter every once in a while. The engine has never stalled. If I turn the air conditioning on, the warm idle problem goes away and the idle is steady at about 800 rpm.

The Haynes Manual gives a couple of suggestions (PVC and one other I forget). I have checked both and they seem fine.

The engine starts well once it has warmed up (even a little).
The engine runs fine at all other times, no misses etc..
This problem has just started recently.

Any suggestions regarding the cold start or warm idle problems would be appreciated.

PS. I read this forum often and am impressed with the knowledge out there, especially from a few of the regulars.

Thanks in advance.
 

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Probably the CHTS

I am going to suggest that the problem you are experiencing is due to a failing "Cylinder Head Temperature Sensor" (or CHTS). This is a little sensor and harness on the front of the engine that reports the cylinder temperature back to the ECU and uses it to make adjustments (fuel and air ?).

You can get a replacement from Nissan (sensor itself) for about $33. Replacing it via the Haynes Manual method is a lengthy job although not necessarily a difficult one. There is a suggested method on z31.com that I haven't tried yet (will be soon) but have heard it works and it's much easier.

Here is the link for the "easy method":

http://z31.com/repairs/chts.shtml (courtesy of z31.com)

Here are two pictures of the CHTS and harness with many parts out of the way courtesy of JohnZboy.




Run your ECU codes before purchasing anything (see your Haynes manual) and it should tell you for sure whether or not the CHTS is your problem.

Good luck!



Post Edited (Aug 2, 1:34pm)
 

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Discussion Starter #3
To Stu85na:

Thanks for the prompt response.

I had someone else suggest that it could be a leaky vacuum hose.

What do you think?

Great pictures. I wish my engine looked that good.
 

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I wish my engine looked like that to :). I can't take any credit - that is JohnZBoy's engine.

If you are unsure your best bet is going to be to *run the ECU codes.* They will tell you for sure if your CHTS is not responding.

There is a procedure for running the ECU codes in the Haynes manual. If you don't have one pick one up - it is probaby your most invaluable tool when working on your Z!

I was motivated after posting yesterday and I went ahead and followed the FAQ on z31.com. I've had the part for a while but I had been waiting to put it in. I can say that the method does work but you should expect to replace the harness because the fitting is old and crumbling. It is much easier than the suggested Haynes manaul procedure however!

I am waiting for the sub-harness to come in from nissanpartscc - should have it Friday! I'll post back here when I get it finished.
 

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I would try some injector cleaner, could be dripping injector over night? also fuel system could be loosing "rest" pressure over night. It should have residule pressure for quite awhile after shut off. Verify fuel pressure per the manual.
 
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