[Unknown User]

I have a 1979 Datsun 280zx that I absolutely love. My battery had died and so I got it charged up, and when I put it back into the car, the idle was at 2000 rpm (reg. 900-1200) and when I was in motion and started to brake, my car would be at about 3000 rpm, then would fall to about 2000 again when I was fully stopped. My battery wasn't charging either so i got a new altenator installed but my car is still idleing very high...and idea what it might be, I would really appreciate it!!

Thanks,

Jon

 

[ConorP]

I don't think the two problems are related. High idle can be caused by lots of things. Check your Dash-Pot first, most of these are broken anyway, you can remove it with two screws and you won't even notice it missing. They can jam and cause high idle. Check for cracks in the air hose between the Air Flow Meter(AFM) and the Throttle Body. Also check the hoses on the Air Regulator for cracks.

> I have a 1979 Datsun 280zx that I absolutely
> love. My battery had died and so I got it
> charged up, and when I put it back into the
> car, the idle was at 2000 rpm (reg.
> 900-1200) and when I was in motion and
> started to brake, my car would be at about
> 3000 rpm, then would fall to about 2000
> again when I was fully stopped. My battery
> wasn't charging either so i got a new
> altenator installed but my car is still
> idleing very high...and idea what it might
> be, I would really appreciate it!!

> Thanks,

> Jon

 

[Unknown User]

> I don't think the two problems are related.
> High idle can be caused by lots of things.
> Check your Dash-Pot first, most of these are
> broken anyway, you can remove it with two
> screws and you won't even notice it missing.
> They can jam and cause high idle. Check for
> cracks in the air hose between the Air Flow
> Meter(AFM) and the Throttle Body. Also check
> the hoses on the Air Regulator for cracks.
Check the air regulator for leakage when the car is at operating temp. take a pair of pliers and pinch closed the hose that goes to the boot between a.f.m. and throttle body,if the idle drops down significantly, it's bad, happened on mine
.

 

[Don]

> Check the air regulator for leakage when the
> car is at operating temp. take a pair of
> pliers and pinch closed the hose that goes
> to the boot between a.f.m. and throttle
> body,if the idle drops down significantly,
> it's bad, happened on mine
> .
The first thing I would have checked would be the BCCD. That's quite often the culprit for sustained high idle particularly when coming to a stop. If it's a constant high idle (and you're running rich) check your temp sensor. The BCDD would be my bet. You can make an adjustment on it to lower your idle.

 

[Buddy]

> The first thing I would have checked would
> be the BCCD. That's quite often the culprit
> for sustained high idle particularly when
> coming to a stop. If it's a constant high
> idle (and you're running rich) check your
> temp sensor. The BCDD would be my bet. You
> can make an adjustment on it to lower your
> idle.
Jon,
The last reply (Don) is probably your best bet. I had the same problem last yr w/my '80zx. I actually replaced the BCDD (Boost Control Deceleration Device) which is attached to the throtle body. I did try to adj the bcdd but the adj was only very suttle to fix the high idle. BCDD is not a cheap part.

 

[Russ83ZXna]

How much did it cost and where did you get it from. Mine had the same problem and i closed off the vacumn lines and the end that goes into the intake.

> Jon,
> The last reply (Don) is probably your best
> bet. I had the same problem last yr w/my
> '80zx. I actually replaced the BCDD (Boost
> Control Deceleration Device) which is
> attached to the throtle body. I did try to
> adj the bcdd but the adj was only very
> suttle to fix the high idle. BCDD is not a
> cheap part.

 

[Buddy]

> How much did it cost and where did you get
> it from. Mine had the same problem and i
> closed off the vacumn lines and the end that
> goes into the intake.
The BCDD cost me $237 from NISSAN. I also had a wierd bell sound comming from the BCDD when I decelerated for about6 months prior to it going out. Please note that there are two applications for the BCDD '79zx, California or Federal zx model.
The vacume lines you are talking about, are they attached to the throtle body? If they are these lines hook up to your distributor vac. advance and you vacume switch located in the front of the
head. Since you modified them, does your dist. still advance? This may cause high idle..Let me know...

 

[Russ83ZXna]

Wow that is expensive.

This is the way I plugged the bcdd

i plugged the vacumn line that comes from the top of the intake.

took the bcdd off the intake and put a dime into the top of the bcdd (the dime fits tight in that spot)
put a screw into the larger vacumn line that connects to the idle adjustment screw.

My car is an 83 so there probably a difference on how they are connected.

When i took the bcdd out of the loop the idle dropped a good 300-400 rpm's.

the other thing i did was i connected the vacumn advance directly to the intake.

> The BCDD cost me $237 from NISSAN. I also
> had a wierd bell sound comming
> from the BCDD when I decelerated for about6
> months prior to it going out. Please note
> that there are two applications for the BCDD
> '79zx, California or Federal zx model.
> The vacume lines you are talking about, are
> they attached to the throtle body? If they
> are these lines hook up to your distributor
> vac. advance and you vacume switch located
> in the front of the
> head. Since you modified them, does your
> dist. still advance? This may cause high
> idle..Let me know...