strange idle issue 78 280z

[klork]

So I have a weird idling issue with my 280z. It idles fine when cold and at a stop but once the car warms up and say I push the clutch in to come to a stop the engine will idle at around 2000-2200 rpm until i slow down to around 2 or 3 mph. I have 2 short videos showing the problem.

video 1

video 2

[klork]

Anyone have any ideas?

[stwrangler]

my bad,didn't know it was stock, couldnt open videos.

Edited February 23, 2010 by stwrangler

[cygnusx1]

BCDD valve.

[NewZed]

So I have a weird idling issue with my 280z. It idles fine when cold and at a stop but once the car warms up and say I push the clutch in to come to a stop the engine will idle at around 2000-2200 rpm until i slow down to around 2 or 3 mph. I have 2 short videos showing the problem.

video 1

video 2

 

I had a similar problem with my car. Here is a wordy description -

 

That thing you're pointing at that "might need a vacuum line" is the dashpot. It does not need a vacuum line, it is just open to atmosphere. It is designed to hold the idle up when downshifting or lifting the throttle, for emissions purposes mainly, as described in the Emissions section of the FSM.

 

The dashpot can get stuck or sticky. Mine needed adjustment due to wear (76 car). The plunger had dropped down and was hanging up below the pad it sits on, holding the throttle open and giving a high idle. It took a while to figure out. I had to lift it up to the limit of play in the mounting bracket to get the plunger back on the pad. Work the throttle from the engine bay with the engine off and you'll see how it works, and if it is close to hanging up or not.

 

Some people just remove it but I have found that the car shifts smoother (for casual cruising) with it on and adjusted. I adjusted mine for driveability, not according to the FSM procedure.

 

You may also have a light throttle spring, or one broken (as I did also), allowing the throttle to hang. There are two springs pulling the throttle closed, one around the throttle body shaft and one underneath it connected to the linkage. The one underneath on mine had rusted and broken. It is difficult to get to, and hard to see, so the previous owner had stuck one on the linkage on top, which did not work well. I put an Ace Hardware spring in the proper spot. You might have to try a few different strengths and lengths to get one you like.

 

There are also lots of joints in the linkage that can dry up and stick.

Edited February 23, 2010 by NewZed

[cygnusx1]

B-C-D-D Valve.

 

http://forums.hybridz.org/index.php?/topic/70142-bcdd-removed-now-backfires-at-downshift/page__view__findpost__p__673663

[klork]

Thanks for the info. Ill look into both of those but it sounds like the bcdd valve. Anone have any ideas about my tach from what it does in the vid? Im assuming its dead but not 100% sure.

[supra240z]

Thanks for the info. Ill look into both of those but it sounds like the bcdd valve. Anone have any ideas about my tach from what it does in the vid? Im assuming its dead but not 100% sure.

 

ya time for a new tach. before you do if you have a friend with a cheap tach hook the signal wire up to it and see if it does the same thing. if so you have other issues.

[klork]

I have one I can barrow out of my Camaro.

[klork]

Ok so update on my problem. It was the BCDD valve. The valve is actually working correctly as far as I can tell. What seems to be malfunctioning is whatever sends it the 12V signal to close it. At idle it has 12V going to it but once I start moving and its warmed up it doesnt have power untill I come to a stop. So I found if I hook a constant 12V source up to it the idle problem goes away because the valve stays closed.

[Daeron]

Have you read my post about the EFI bible?

 

I never hesitate to recommend re reading the sections relevant when trying to diagnose a component that has failed like this (ie, thingy works, but the car isn't running thingy right) and I do it myself.

 

While I'm not personally an extremely religious man, i will say it is called the Bible for a reason: just like the Holy Bible, it is a book that can never be finished sharing its wisdom with you. Christian worship (especially today, in America) is largely based on analyzing the wisdom of the Good Book for the nth time, and the EFI Bible works about the same way. Read it through, read it again, then refer back to it without hesitation for guidance with your issues.

 

Now, like I said, I'm not too religious myself, but I sure understand enough Christian theology to know that the metaphor holds. If you read this and you're a churchgoer, then you understand, but if you are more towards the cynical side, I tried to make it clear.

Edited March 10, 2010 by Daeron