1976 280 Idles Rough

[CnoB]

I have a couple issues with my 280Z. When started cold it has a rough idle, between 400 to 900rpm but after warmup idle is 700 and seems to run rich.
When slowing down( gearing down ) engine seems to slow down car till about 2,600 rpm and holds that rpm till almost stopped, hard on brakes and fuel.
Does anybody out there have any suggestions. I have original Datsun shop manual as well as Chiltons amnual also.
I am mechanically inclined and have already replaced suspension and most all bushings.

Thanks in advance
Cnob a.k.a...... Chuck

[Ont240]

How clean is the throttle door, free movement?
and how freely does the air door open/close?
Air filter?

[CnoB]

Hi Ont24
Both doors seem free and installed K&N in original air cleaner box, checked for vacuum leaks and only found the oil filler cap to have no gasket, could it be that simple??
If I understand my service manual suspect parts include , thermo sw, temp sensor, AAR, cold start valve and BCCD system. Need to get @ some meter checks @ the 35 pin connector.
Laid up a bit right now with Knee replacement but will post findings when able to move a little better.
Thanks
Chuck

[dutchie3]

air flow regulator could be stuck open...could be a sensor like you said, cold start system although that normally only really affects warm up when car is reeeealy cold ie winter. Oil filler cap thing to find vacume leak wont work if it is a leak at an engine gasket, manifold etc. Running rich could also be temp sensor or AFM.

[CnoB]

Thanks dutchie3
I am still a bit limited as to flexibility and kneeling. This "bionic" 1/2 knee joint is taking it's time and Zed weather is here. Moving son home from Vancouver end of May and we'll be getting at it for sure then. He wants to drive it so he needs to help the old man a bit first, I am an electrician buy trade and know my way around a multi meter, just have to get at the 35 pin connector and do some checks so the manual says, I will post findings but probably not till son is home, I just look at it and drool. Thanks for all your advise and look forward to meeting some of you in the near future, I live in Peterborough so maybe when there is a tour around here it will be ready.
Regards
Chuck...a.k.a....Cnob

[flyzlo]

If I recall correctly there is a BCDD that's main job it to hold open the throttle until the gas burns off. It was put there to compensate for a quick slow down. I think it looks like a dash pot with a rod joining to the throttle shaft. Check that and make sure that it is operating correctly. Maybe you can disconect and test drive to see how this affects your high rev.

[CnoB]

Thank you for the advise. I think that you are the first person that has had a suggestion about the revs hanging up when down shifting. I will check these things out shortly but right now I have a lot on my plate so please be patient and as soon as I have time I will check out these things and post my findings. Looking forward to meeting some of you guys and gals on a road trip in the near future.
Thanks again
Regards
Chuck Beach

If I recall correctly there is a BCDD that's main job it to hold open the throttle until the gas burns off. It was put there to compensate for a quick slow down. I think it looks like a dash pot with a rod joining to the throttle shaft. Check that and make sure that it is operating correctly. Maybe you can disconect and test drive to see how this affects your high rev.