ZCar Forum banner
1 - 4 of 4 Posts

·
Registered
Joined
·
27 Posts
Discussion Starter · #1 ·
Hi Fellas,

Been I while since I had a Z31 or used the forums. But I'm picking up another one soon. The car was garaged and there's no rust on the body, but it's hard to start and idles rough when cold. Drives fine when warm. Fuel injector recall was performed and t-belt was done at 58k. I didn't think to ask the owner if it had a tune up, but from what he says his uncle was meticulous about the car.

I remember this being a common problem with these cars and once read it could be the CHTS or the Idle Air Control Valve. Would appreciate any additional input or advice as I'd like to get her up to speed by fixing the idle problem asap.

Thank you
 

·
Registered
Joined
·
2,370 Posts
First thing that I would do is start at the ECU. Remove the three plugs and insure they are not corroded or broken and also check the contacts on the ECU outlets. Sometimes these can be dirty, corroded, or even unconnected, causing issues. This in itself might just reset the system and work better. (like it does on a late 280zx) Just make sure that whole area is secure.

Next, run the ECU diagnostic checks via the FSM. Now, each year is a bit different in the steps, but its not hard on the 84. You will have to read the book to find the codes. Simply remove the ECU from its housing and keep the plugs connected, and you will use a flat head screw driver to turn the diagnostic screw. Lights in the little exposed hole will indicate the status of the systems check on each component specified. Again, you need to read the section in the 84 FSM to know what the code readings are.

You could possibly have in issue with the Idle Air Control valve, but I doubt it. If it hasn't been messed with, you should be good there. There is an adjustment screw that you can adjust if needed. Also might be of use to remove the valve and make sure it is clean inside and not blocked or corroded. Again, I would only do this if needed. The valve on the turbo is a bit different than the valve on the non-turbo car. Unplug the harness on it and make sure it is clean and not corroded.

I think you may have an issue with the AAV (air auxiliary valve) or cold start valve I believe. Your ECU diagnostic will tell you if this has failed. You can also remove it and inspect.

Vacuum leaks- check all the hoses under there and make sure they are all in good order and not missing.

Fuel pressure regulator - make sure the hose on this is good and that the valve is working as it should (via FSM)

MAF - it probably wouldn't hurt to remove this and inspect the inside. Make sure that element isn't blocked or covered in anything... Inspect the plug harness too.

Plugs and electrical connections - make sure to disconnect and inspect all plugs and harnesses you can find. Make sure they are clean and not corroded, and reconnect tightly.

Check your battery, ground, and starter connections. Also, you can try starting it and running with the A/C off...
(when its on load, the idle control valve automatically adjusts for higher idle)

Lastly, be aware the the 84 and 85 cars both T and NA had a common lean running issue at first startup of the day.... Its the ECU. Normal.
Nissan seemed to have fixed this on the 86 model. My 84 AE turbo did this. The only thing you can do is, let it idle and run for a few minutes before you take off. If you just start it up and hit the gas, the car will stumble, buckle, and hesitate. Just let it warm up a bit and then you'll find when you start driving, everything will be very smooth (pending there are no other weird issues with other components). My 84 would run great after a few minutes (first start of the day) and keep running great all day long. Again this is a common issue on early Z31's. My 87na never had this problem....

I've had two of these things and they both had nearly the same issues. Just my experience. Good luck and enjoy!

Bon
 

·
Registered
Joined
·
27 Posts
Discussion Starter · #3 ·
Hi Bon,

Thank you for your reply. You did a nice job covering everything in a very detailed manner. Moderators can we get this stickied for future reference? I forgot that the 84-85T runs lean on startup. I was also wondering if it could be the crank angle sensor since it's hard to start although the Idle Air Control Valve can cause that too.

Thanks for your wishes. Hope to have the car soon. I'm going to have it transported home because people on the route 80 drive crazy.
 

·
Registered
Joined
·
2,370 Posts
Do the ECU diagnostic checks to see if the CAS is failing or not. Don't start throwing parts at it. Diagnose things first.
 
1 - 4 of 4 Posts
Top