1977 280z Rough Idle

[Yaboyolin]

Hey everyone, I've got a 77 Z 2+2 right now and I'm having some issues. The car simply won't idle or if it does it runs really rough at 500 RPMs. It revs up and drives fine, but if I stop it usually dies. I tried the simple thing, to adjust the idle from the idle screw, but the idle will not raise up or lower. It has a sweet spot where it runs best, but 500 RPMs is where the engine is determined to idle. The fuel regulator is hissing. I checked the vacuum line for gas and there wasn't any noticible amount, but I'm pretty positive it shouldn't make that noise. The AFM is new, as the old one wouldn't let the car run at all. There isn't any black smoke or anything of that nature when the car dies. It just sputters and dies. I've read to block of the auxiliary air thing, and will be doing that today, but was curious if any of you had other ideas? 

[SteveJ]

What is the fuel pressure? Are you sure all of the injectors are firing? Are you getting spark to each cylinder? Was the car running at any time with the old AFM? Did the car have this problem when you bought it?

[Zed Head]

Sounds like vacuum leaks, especially since you can't adjust idle using the set screw.  The engine has to be completely sealed, including the PCV system and all gaskets, even the dipstick tube and oil filler cap.

The hissing from the FPR is normal, it's just the fuel passing through.

[siteunseen]

If you've changed the afm make sure there's not a crack in the accordion boot. Its easily done to forty year old rubber. 

[Yaboyolin]

The fuel pressure is 35 or so PSI. It sure seems they're all firing, it runs great above 750 RPMs. The car would run for 10 seconds or so before dieting with the old AFM. I'll check for vacuum leaks as well.

[SeKcGamer]

My z did that not to long ago and I just fixed it by cleaning the distributor cap points and it started to idle just fine. After two days I bought a new rotor.

Sent from my SM-J320V using Classic Zcar Club mobile

[Yaboyolin]

So I did find a vacuum leak. A rather big one at that. The first picture is a hose that's directly under the intake manifold. The picture might be upside. The second picture is of my current setup. Where dose the hose in the first picture go? If I hold my finger over the hole the idle gets real rough. The third picture is of what I assume to be the PCV valve

 

[SteveJ]

That is the positive crankcase ventilation (PCV). It should go to your intake.

Download a copy of the FSM if you haven't already. The link is in my signature. The information to start you off is in the EC section.

There should be a hose from that tube that has a steel mesh (anti backfire) near the tube and a PCV valve at the other end of the hose. The PCV system should go into the intake downstream of the AFM, so if it open, you have a big vacuum leak in your intake.

[Zed Head]

The PCV valve is screwed up in to the bottom of the intake manifold, about centered, away from the engine.  There's a space in the heat shield for it.  It would be to the right in your pictures of the crankcase vent tube.  That tube should have a hose running from it to the PCV valve.  We can't see the top of your valve cover.  It might have a little breather on it because somebody deleted the PCV hose.

You're probably lucky that you have a new AFM.  Don't adjust anything on the AFM, get the hoses back where they should be, and you should be back in control, using the idle speed bypass screw on the throttle body.

Good luck finding the hose.  You could probably make a water hose work for a short while, for testing and tuning, but it's a very high heat area and the proper hose is designed for it.

[Zed Head]

SteveJ, you should put the link to the classiczcars Download section in your sig.  Keep things in house if you can.

http://www.classiczcars.com/files/

 

 

[SteveJ]

Something like this in the proper diameter might work: https://www.summitracing.com/parts/vpe-20442/overview/

[SteveJ]

12 minutes ago, Zed Head said:

SteveJ, you should put the link to the classiczcars Download section in your sig.  Keep things in house if you can.

http://www.classiczcars.com/files/

 

 

I'm old. I don't remember the links here.