79 280zx: Fast Idle 2200 RPM

[siteunseen]

@madkaw is doing something similar.  He may shed some knowledge he's picked up?

[Captain Obvious]

Cool. Glad you got to the bottom of the issue. I second the call for an autopsy of the screwy throttle body. Send it to me if you don't want to do it yourself. I'll open that sucker up!  

5 hours ago, Dave WM said:

with BCDD wire attached rev engine up to 3k and then quickly shut throttle. Since the car is no moving the solenoid should be on and the BCDD not active allowing RPM to quickly drop.

Next with the BCDD wire off (simulating above 10mph) do the same, I am expecting the quick shut off of the throttle to generate a high vacuum, activating the BCDD and bypassing some air, there by keeping the RPM up at least a bit (with the car not moving the vacuum will not sustain long anyway so I don't think it would hold it up very long).

Dave, I would expect the same thing. With the wire off, you might discern a longer time to return to idle if you blip the throttle. Probably not a lot longer, but you might notice some difference.

While you were in there messing around, were you able to determine if there was any change in idle speed with the wire connected vs. disconnected?

[Dave WM]

really hard to tell, I know it is different now that when I 1st got the car, it used to hang up on idle until right at 10mph then it would drop off. Anyway I took it out for a spin and honestly I could not tell the diff with the wire on vs off. Rev up to 4k in 1st the suddenly get off the throttle, plenty of engine braking for a second or two, then it would relax just a bit.

 

Before it would just sail along slowing down very little until 10 mph then it would drop of fast.

rev up with car still and connect the wire and no wire, again no real difference in drop off from 3k to 800

I can hear the solenoid clicking away when I connect and disconnect so I am pretty sure that part is working. Maybe there is a hole in the chamber that is suppose to react to the high vac and pull the bypass open?

[Zed Head]

I think that the proposal is (at least mine was) that disconnecting the wire would change the quantity of air bypassing the throttle blade.  Significantly enough that it would change idle RPM.  Not while driving but while sitting in neutral.  Unplug wire idle changes, plug it back, it changes back.  It was just a thought that it might be one cause of the BCDD causing a high or a low idle.

The "relaxation" that you feel is the fuel coming back on at 2800 RPM.  All the car reviewers hated it.

[JSM]

1 hour ago, Captain Obvious said:

While you were in there messing around, were you able to determine if there was any change in idle speed with the wire connected vs. disconnected?

Yes I did unplug it. Made no difference.  I could not discern if the selinoid was activating or not. Kinda hard with the engine running so fast. 

Edited January 27, 2017 by JSM

[Zed Head]

But the one you unplugged was the messed up one, right?  I think that Dave might be the other guy that could have unplugged his BCDD.  Some day I'll unplug mine and see what peahens (picked the wrong suggestion.  You know what I mean).

[JSM]

37 minutes ago, Zed Head said:

But the one you unplugged was the messed up one, right?  I think that Dave might be the other guy that could have unplugged his BCDD.  Some day I'll unplug mine and see what peahens (picked the wrong suggestion.  You know what I mean).

Yes the 79 had the wire like the earlier Z cars. The 80 I put on was only vacuum actuated, no wire. One less thing to deal with honestly. 

[Dave WM]

agree with the throttle cut is prob what I am experiencing (seems to be the RPM ranges I am feeling the effect in). I am pretty sure the BCDD is doing nothing at this time, but at least its stuck in the no bypass mode.

Edited January 27, 2017 by Dave WM