[z_man300]

Seems like every time I go on a long trip, I get this problem:

When I stop after cruising for a couple hundred miles, my 79's idle is HORRIBLE when I restart. It either idles at just over 500rpm, or I have to add gas just to keep the engine running, and then it sputters. Once I drive say, a hundred feet, idle returns to normal.

Opinions? Fuel vaporization maybe? Car runs perfectly at any time other than a hot restart.

 

[greydog]

I think you're right on target. I have a similar problem (maybe not as severe) but irritating. Only things I know of are to try to isolate the fuel line from heat, make sure your heat shields between the intake and exhaust manifold are in place, place a nonconductive washer between the fuel line hold downs and the bosses on the manifold, etc.
I live in the Pacific Northwest and the problem is worse in the summer. I rigged my injector cooling fan to run every time the ignition is shut off; seemed to help some. Now that the temperature seldom gets over 60 degrees, I've gone back to the factory setting.
I think the problem won't go away completely because of the engine's design (intake and exhaust one on top of the other). If anyone's got a good workable fix, maybe they'll let the rest of us know.
Dan

 

[Ed79ZX22]

I am the orginal owner of a 79 and had the same problem. Mine started after one winter in Missouri and I changed the t-stat with a aftermarket one when the car would not heat in the winter. The next summer I would drive for awhile and on a hot day after the car would sit for 15 min. or so, then start it up it would do the same thing untill water started to circulate. I started to notice the temp. gauge was going up to the inside mark on the hot side. After I moved to Florida I was having the same problem when the outside temp was above 90.

To fix my problem I flushed out my cooling system, replaced the rad. cap & t-stat with Nissan parts, the t-stat I used was the 170 degree one. What I noticed is the aftermarket t-stat was not made like the OEM and looks like it would get hung up or not open all the way like it should.

I only have the problem once in a great while after I have being running 80 MPH plus for awhile. Mine still has the orginal rad. and from what I have learned from this site is that once you change the rad out to a 4 core rad., the cooling system works better.

Search under cooling and there is a lot of info out there.

Enjoy your ride

 

[ram75280z]

I have noticed that slight adjustments of the idle speed screw can affect this symptom. Don't ask why but just having the screw in different positions even without any real change in idle speed. It either does it every time when I restart the car after a brief period of rest, like refueling, or with a slight adjustment it rarely happens at all.

On some cars with ogygen sensors this problem can be caused by a bad O2 sensor. I also own a 79ZX but it doesn't have a O2 sensor so I think yours would only have one if it was a California model.

Try making the slight adjustments to the idle screw. I believe the reason that it affects the idle is because the position of the idle screw determines how much air is drawn through the air-bypass. The air-bypass is what alows the engine to have a high idle when cold. You will notice, if you listen at the air-filter opening, when the screw is turned the sound comming from the air-filter will change in pitch (sounds like it is sucking in more air). I have found that the louder the sound the more air will be drawn throught the air-bypass when the engine is cold.

It seems that there is a couple of points in the screws travel where this "louder" sound occurs. You should be able to notice the sound change by turning the screw so that the longer of the two slots in the top of the screw is in a 12 and six o'clock position if the front of the car is 12 o'clock. It may already be close to this position. I have found that these cars function noticebly better if the screw is atleast between 10 and 2 o'clock as I described. Make some adjustments until you hear the sound change and drive it for a few days and see what happens. It might take a couple of tries. You might be surprised. It may not totally eliminate the problem but I am sure you will notice a difference. I hope that helps. Ross

 

[280 ZX]

vapor lock

 

[z_man300]

Thanks everybody....

Nice to see I'm probably on track. Like Ed, I just installed an aftermarket thermostat. Mine's from NAPA, and all they sell is the equivalent of Nissan's cold-weather t-stat, which means my engine's been running hotter than previously. That's why I suspected things might be heating up a little too much under the hood; not quite enough for the injector fan to come on, but enough to cause problems apparently.

I just bought a normal temp Nissan t-stat, so I guess I can live with my problem for now till I'm ready to swap t-stats again next spring.