duowing

So yesterday it was ridiculously cold, somewhere between -5 and 5 degrees Fahrenheit. Well I tried to run my Z, and it was running awful, it did ok at first, but shortly after it started stalling on me. It would idle and turn over, but if I gave it throttle it started acting like it was running extremely lean, then would just stall out. I couldn't even get the car back into the driveway as it would just try and go then stall. After a little while it seemed like it must have started to warm up as the car started to go ok again and make it's way back into the driveway almost as if nothing happened. I have no idea where to even start with this, maybe it's just due to the extreme temperatures. Any advice on this one guys?

terrymac

I experience the same problem fall of 2007.
I thought that the Cold Start Fuel Injector
and Aux Air Valve needed to be compensated
for by the AFM.....(No Way)

After allot of trial and error, and reading
the FSM manual, it turns since the FI engines
don't have High Idle Cam like carburators,
soo you put more fuel into the Zs engine, Then
add more AIR/O2 (Aux Air Valve). The engine
will run a bit faster about 13-1400 RPM during
Cold Starts.

The Zs ThermoSwitch is used to control when cold
Start Fuel Injector is powered ON, and stays
ON until either Engines Coolant Temp or its
Internal Heater Coil causes the Fuel Injector
Circuit to Open.

There is another Heater Coil in the Aux Air Valve.
So we have a Race who will Win, Fuel Injector
turns Off early, engine will stall, if its on the
road, as the Aux Air Valve is dumping too much
AIR/O2 into the engine, mixture too lean.

Or if the Aux Air Closes, but the Cold Start
Fuel Injector continues to pump-in more gas, the
exhaust will suddenly be Black and engine may
sputter or Stall. The extra fuel will foul the Z
Spark Plugs. I switched to Hotter Plug, winter
only.

I would hope that both Close (aux air valve),And
Cold Start Fuel Injector Stops with the extra fuel,
about the same Time.

That ALL I know about Cold Start...I am in process
of buying another Aux Air Valve.

Hope the about info helps!

Terrymac

duowing

Two things that are a problem with my car, the air regulator is faulty, when closed it leaks, and when open it doesn't close as it should. The bimetallic spring with direct voltage takes a very very long time to close, so I've blocked off the air regulator, also my AAC valve is basically left open passing alot more air. What I'm going to try is connecting the AAC up to direct vacuum, to keep it closed, until at least the weather warms up so I can block-off my AAC, and in the meantime just manually open and close the ball valve I put in place of the air regulator.

terrymac

I don't know how connecting the AAC to vacuum will balance

the engines fuel air mix when cold and when Warm without

adjusting AFM ?

How did you block-off air regulator air flow ?

duowing

I used a 1/4" ball valve I got from the plumbing section at home depot. I was able to recreate the situation today, and by opening up the ball valve it seemed to correct the problem, then when I closed it, it went back to basically being undriveable. Now the bad part is once the car warms up you basically need to park pop the hood, close the valve, then get back in the car otherwise it's passing so much air that it's like I'm running the car at 2000 RPM at idle, only my throttle isn't open and causes a leaner condition, but the car is much more tolerable this way since I'm really only using it for really short drives to work, and with the temperature it's barely enough for the car to warm up.

terrymac

Sounds like you have found the guilty party...

I found mine by clamping the air regulator rubber
air hose with a pair of vise grip pliers.

Your Z may need a Air Valve too since you are
driving it daily.

Best of luck & enjoy the drive!

Terrymac

FubarI33t

Or all of you can just do what I did. Take all the crap off. Even cold start. 17°F out and she still starts right up. No cold start, no air regulator no notin. Idle is controled by screw on TB. Ahh crisp throtle response too.

duowing

So you just idle the car up when cold, then turn it back down in the warm weather? That could be my problem, that I'd almost need to adjust the throttle stop for when cold to get more air to pass through. Although this should be the only winter that I'll be driving the car through, as spring/summer I'm planning to swap into an S30 and then use it as a good weather driver.

plainwhiteZ

"No cold start, no air regulator no notin. Idle is controled by screw on TB. Ahh crisp throtle response too."

Really? maybe I should take all that crap off too. I live in cali in the bay area, no extreme teperatures here. I gets down to thirty degreees maybe a handfull of time in the winter. I wonder if it is legal here.
the laws are super strict here.

hoov100

honestly cali smog aint that hard to get around.

Niku-Sama

now does it just die when its comming down to idle and seems like it goes to far and stalls or does it struggle all the time?

i have an issue where the car will be fine but when its cold and comming down to idle it tries to die, some times it dies, but it rums fine. i am sure its tied into my idle speed going way up when the car warms up but i have a feeling my problems are related to vaccum advance timing not working right but i dont have a way of testing it at the moment.

i've tested the AAV and Cold Start theyre workin properly, a new coolant temp sensor might not be a bad idea, i am sure it hasnt been replaced and replacing the PCV helped some, i dont get a drop in idle comming down on rpm as much, the old one was gummed up but i am sure it moved better when it warmed up. i am sure leaky injector on #4 isnt helping much either

oh and Cold Start Injector is just that cold start, it shouldnt be running untill the car gets to temp it should just go untill things fire.

duowing

Ok, so I finally got to putting on a good thick steel block-off plate with a new gasket for my AAC valve. I removed the VCV valve, and still maintain my ball valve in place of my air regulator, just a straight hose running from j-pipe to ball valve to throttle body. I need to check more to make sure I don't have a vacuum leak, but now my car idles super low about 600-650 RPM. If not lower and a lot of times it will idle smoothly for a few moments before it wants to stall out. I was allowing the car to idle and adjusted the ball valve little by little to bring the idle speed up, and it seemed to smooth out. So I'm thinking that I may have gotten rid of something that was allowing extra air to bypass the throttle body when it shouldn't have been. So far the car seems to run pretty much the same. I'm thinking that by allowing more air to bypass the throttle body to bring up the idle and smooth it out would indicate almost running too rich. Because doing that would be adding more air without adding extra fuel? Or would it be adding more fuel as well? Sense the TPS or throttle rod wouldn't move, it wouldn't kick the car into off idle mode.

Although I'm wondering with these cars can running too rich also sound like running too lean? I know that lean is through intake and rich is out of the exhaust, but with the exhaust and intake manifolds right near each other, when the fuel ignites in the exhaust manifold, couldn't that have the same sound as popping through intake?

As far as that running issue went, I've just left the valve open on cold days and I have no problems, but if I close it off idle drops real low, gets shaky, and has a lot of problems until the car kicks into warmed up mode. I'm also using the Z31 ECU/MAF which may cause some differences.