changing idle

[zeiss150]

Hey guys. I've been fighting this problem since I got the Z 4 years ago. The Z idles at about 850 RPM's wich is great, nice and smooth. once I start driving around the car will jup up about 150 to 200 RPM when I come to a stop light. If I tap the gas peddle, the idle will slowly (in about 1 to 2 seconds) drop back down to 850. the Z runs smooth as a top at both RPMs but I would like it if it were a constant 850.

Is this a throttle shaft problem? the shaft bushings have never been redone. The chrome on the shafts is worn. there is nothing binding or hanging up in the linkage, so thats not the problem. My carbs are supper clean I pretty much rebuilt them with the exception of the throttle shafts.

So What do you guys think?

Thanks for your Help, Matt-

P.S. I came accros another Z guy and he said he was having the exact same problem.

[Zup]

Matt---

My 2/73 build date 240 with 72 roundtop carbs is the same way. I adjust idle to 850 and after driving come to a light it's at 1000. I attributed it to the dizzy not having a working vacuum advance----but I don't really know.

This is with ZTherapy rebuilt carbs from 98 so I am pretty sure it's not a throttle shaft wear problem!

The car has had all of the emissions stuff removed----no ABV, no vacuum diaphrams for controlling the decelleration, etc. Recently rebuilt and runs very strong otherwise.

I am left suspecting a slight bind somewhere in the linkages, even though I have lithium greased all the bellcranks and sockets/balls and adjusted the carbs many times it persists. Sometimes a foottap brings it back down, or a light engagement of the clutch, but not always.

I still love it!!

Let me know if you get the cure cause I definately have the same disease! :sick:

Jim D.

"Zup"

[astrohog]

I had a similar problem last summer, although mine was a little more extreme, so I am not sure this solution will work for you. My idle would "stick" so high that it would actually keep climbing past 4,000 RPM's and I would eventually have to turn it off before it would redline. What I found was (not sure of all the correct terminology here, so bear with me) that there is some sort of "idle slow return" located on the throttle/carb linkage that is supposed to slow the drop of RPM's during an upshift for a "smoother" shift. When this went bad on my car it gave me fits!!

I spoke w/ others here on the forums and locally and I came to the conclusion that it could be completely removed with no ill effects.

Hopefully some other more experienced members can jump in here with the correct terminology and maybe even some pictures. Not sure if this is the cause of your problem, but it worked for me!

Good Luck!

Regards,

Astrohog

[zeiss150]

thanks for the posts guys. I have also taken all of my smog stuff off. I plugged all of the holes on the ballance tube so there is no vaccum leak in that area. I've also replace the balance tube gaskets. I have a rebuilt ZX dizzy and the vaccum advance is working as far as I know.

It almost seems like the problem is because the butterfly valve in the SU doesn't go compleatly closed, so when you tap the peddle the quick up down motion makes the butterfly valve "close" a tiny little bit more. Stupid idea?

If anyone has anyother ideas ... Bruce... please jump in.

Matt-

[beandip]

astrohog, I believe the name is ''dash-pot'' don't know why, and yes just remove it. My Z has just started the same thing, that is idleing at a higher rpm after driving . I haven't started to look for the cause . Seems as it is a common problem . I have zero emissions equipment on this engine , so that is not the trouble. It has just started do in this in the past couple of days. I had the linkage completely off the car when I was refreshing the car. All has been good since then , until now . I suspect the pivot mounted at the dash where the linkage attaches from in side the cabin. Like I said I haven't started playing with it yet. And it is NOT ignition related . Gary

[Zs-ondabrain]

Did any one mention tightening the return springs? Mine did the same thing and everytime I tapped the gas peddle, it would drop down again.

I just undid the springs from the heatsheild, cut a few turns off it, made a new loop and re-attached it. I haven't had the problem since then.

JM2CW

Dave

[zeiss150]

Thats a great Idea Dave. Why didn't I think of that. It would pretty much do the same thing as taping the peddle. I'll give it a try.

Keep the ideas comming!

Matt-

[zeiss150]

Ok so I finaly go around to trying Daves fix (cutting the return springs) and it seems to have fixed the problem!

Now it runs a nice solid 850 rpm (after setting the idle) If I tap the peddle it still stays at 850.

Nice job Dave!

I took off 5 turns off the bottom of each spring, its a pretty easy fix.

Its always the simple things that seem to frustrate us.

Matt-

[Zs-ondabrain]

That's what I thought, Simple is almost always the best way to start. Then go to the complicated way.

Glad to hear it was as easy as I stated.

Dave.

[beandip]

Well I found the solution on my car , I just lubed all the rotating portions of the throttle linkage and the plastic connectors . She no longer has any other idle positions . Just the one that I have set. Shortening the springs will also do it , until it binds further . Gary

[New-to-240z]

can u guys point me in the right direction to adjusting the idle oin my 73 z with flat tops? My car drops to 500 rpms almost everytime when i come to a light and it sounds like its going to die!! Its and A/T, but i would think it would be the same procedure. Anyways, let me know.

[Maddos]

AHHh. Now that you mention it, when I just fitted the extractors had to bend up the heat shield a bit to clear which had the return springs fitted to them. Could be my answer also.