Another simple ? needed to be answered re: idle speed

[sleepy-z]

Im young, my car is older then me. 1975 280z EFI. My simple question is regarding the idle speed when I start it cold, should the engine warm up and have the speed drop as it warms or does the idle speed remain the same warm or cold? It starts at 800-1000rpms cold and runs the same, is that correct or is something wrong? Sorry for the newbie question this is my first pre-90 Z and I want her running right it just seems odd that it doesn't idle high cold and drop as it warms up.

Thanks

[DatsunZsRule]

When warmed up at idle on a manual trans. 800 is where it should be. When first starting it with a cold motor should be around a 1000-1500 and when fully warmed up, it should drop down to 800.

Where is yours constantly staying at? 1000?

[sblake01]

The idle speed should be higher when it's cold. If you're not getting that, check your air regulator. I'm going to give you the same link that I gave in the other thread. The 280Z Fuel Injection Book. It will answer a lot of questions you'll come across and even though it's more geared to 77-78 it will still quite helpful.

http://www.72hours.net/~zcar/280zfuelinjectionbook.pdf.

[sleepy-z]

I honestly adjusted it to sit at 1000 warm it runs smoother there, I was really wondering if it has a switch or valve that causes it to run higher on cold starts. The idle doesn't seem to change when its cold to warm so im wondering if there is anything wrong about that and what might I do to fix that, my manual doesn't seem to help. I did clean the throttle body and the air flow meter but that didn't seem to do anything. Maybe I will lower it to 800 warm to see if it's higher cold.

Thank you for any help.

[DatsunZsRule]

Definitely after you get it warmed up good, set it back to 800 where it should be. If it runs rough @ 800 RPMs than you have other issues with either the fuel management or ignition. Think about it, if you have it set for 1000 at normal operating temps then of course it won't drop to where it's suppose to be. (800)

Before you messed with the idle speed and it was still @ 800 RPM's, what was the issue? Rough idle? Killing?

[DatsunZsRule]

" I was really wondering if it has a switch or valve that causes it to run higher on cold starts." Yes, it's got a Cold Start Valve that only operates when starting or when the coolant temp. is below a certain degrees. When the coolant is above a certain degrees (sorry can't remember what degree off the top of my head) the Thermotime switch will then break the ground for the Cold Start Valve to kill it.

[sblake01]

I answered that in my post earlier. The air regulator allows more air into the intake during warm up. That raises the idle. As the engine warms, the flap in the air regulator closes and the idle goes down to normal. The cold start valve doesn't do anything to the idle. It just injects fuel to help start the engine while cold. Under 35 degrees C if I recall correctly. The thermotime switch will only operate for 8 seconds max and the signal stops when you stop cranking the starter. It's all covered in the book in the link.

[sleepy-z]

Thanks guys, I was once a newbie for twinturbo.net, now im a newbie for classiczcars.com and have a lot to learn about my 280z. I will play with it a little this weekend.