76 Z starts but will not idle.

[280Vette]

Alright so I've searched around and still cannot nail down the problem I'm having.

I bought a 1976 280Z a few months back, ran and drove fine except for an exhaust leak at the manifold. I swapped the manifold for a header and ever since then it refuses to idle. The car will crank up and start, and it will stay running if you hold the gas and keep it in the upper rpms. But as soon as you let off the gas or try to let it idle it starts to stumble then shuts off. It almost sounds like its not running on all cylinders.

Any idea what could be causing this? I've checked all of the fuel lines, filters, etc. It's not a smog motor and the only major things done to it are an A/C delete and a 5 speed from a 77Z

Here's some pictures of the engine if that helps

http://i.imgur.com/bqR4i7q.jpg

http://i.imgur.com/5SejnLO.jpg

http://i.imgur.com/WYkjXYu.jpg

Thanks in advance, this has been driving me crazy

[Zed Head]

Maybe your firing order is off. I can't tell from the picture, but it doesn't look right. 1-5-3-6-2-4, counterclockwise. The engine will start and run with the plug wires backward, clockwise. These engines will also run on three cylinders, maybe even two.

OR, maybe you have a vacuum leak that is letting air past the AFM vane. There's a switch in the AFM that opens, cutting power to the fuel pump relay, if air flow drops too low.

You might have left a fitting on the intake manifold open. All air must pass through the AFM, except for a very tiny amount for the AFM idle bypass, and the charcoal canister.

[rossiz]

it looks like there's been some work in the hose dept... i'd check the FSM for proper vacuum routing. it looks a little off to me - for one thing, i see a vacuum line going to the top of the throttle linkage dashpot, pretty sure that's just supposed to be open to the air, and that leads me to believe the vacuum line should be routed elsewhere.

after you've checked every hose against the diagrams in the FSM and also checked for leaks (don't overlook the PCV hose underneath the intake manifold - those burn up and cause huge leaks) get a vacuum gauge on it and see where you're at.

vacuum advance is a biggie as well - if not working properly you'll get lousy idle, especially with a leak.

my bet is on vacuum issues - during the manifold replacement it's a good chance you didn't hook things back up correctly. also, i'm not sure about the smog setup on the 76, but check to ensure any smog fittings from the oem manifold are suitably plugged if the header has no such provision.

[280Vette]

Well I checked the firing order, it's correct. I took a look at the vacuum hoses and everything seems to be hooked up. What do you mean by the vacuum line going to the throttle linkage dashpot?.

[Zed Head]

What do you mean by the vacuum line going to the throttle linkage dashpot?.

I circled it for him. That little Sorry game piece shouldn't have a hose attached. The other end of that hose either needs vacuum or supplies it to somewhere.

[rossiz]

what he said - and don't feel bad, i only know about this because i did it too...

did you check the pcv hose? it's underneath the intake manifold, right next to the exhaust manifold and more than likely burnt up.

it really sounds like a vacuum issue.

[280Vette]

Will I unhooked that line. It's connected to a t-coupling. One hose goes to the alternater the other to the throttle body. There's no vacuum coming from it so I'm assuming the end that was hooked up to the "sorry piece" needs to be hooked up to a vacuum source. I cannot find where it would go though.

As for the PCV hose it looks okay, no cracks or anything

http://i.imgur.com/42jf9YC.jpg

[Zed Head]

The vacuum comes from the throttle body. It's called ported vacuum and only sees vacuum when the throttle is off-idle. Throttle closed, there's no vacuum.

And there are no hoses connected to the alternator.

Great that you're digging in to doing your own work, but you should take notes when you take things apart and/or use the diagrams in the FSM when you put them back together. Based on the hoses to the dashpot and the alternator. there may be other things connected not-quite-right. That could be part of your problem. Off the bat, I'd say that your vacuum advance hose to the distributor does not have a vacuum source. Just a guess. Every hose and wire has a specific purpose and needs to be properly attached.

You said that you checked the firing order, but did you check the rotation direction?

[280Vette]

Sorry, not alternator, one hose goes to the distributor.

[Zed Head]

Then the hose with no home probably goes to the charcoal canister. But if it's open the distributor advance won't get its vacuum and you'll have a vacuum leak at the throttle body while driving.

Your 76 might also have the vacuum advance solenoid, which only allows vacuum advance in top gear. Complicating hose routing. That's why taking notes is good. If you're not familiar with how all the various devices work it's easy to misplace something or leave it disconnected.

The diagrams and descriptions are in the Emissions, and Engine Electrical, chapters.

[280Vette]

Well I took a look at all of the hose routing (had to wait for it to stop raining) and the only thing I found was a small crack on the hose between the air flow meter and the throttle chamber. I fixed that and while it doe's seem like it'll try and idle a little bit longer, It still dies.

I also noticed that some of the vacuum hoses don't quite look the same as the diagrams. But I compared the engine pics now, to a picture I took when I first bought the car (and it was running) and everything is hooked up the same. All my previous project cars have been carb'd, kind of missing that right now ha

[rossiz]

my car ran when i got it from the PO but there were a ton of things messed up and huge holes in the vacuum system. everything was compensating for everything else. when i started fixing things and putting them right, things got worse before they got better. it actually took quite a bit of fiddling to get everything back to spec, but it was worth it. before it "ran" but now it rocks.

keep the faith and go back to the fsm vs. what you may have had before. you may have to check other adjustments that were set out of spec to compensate for mis-connected and/or damaged vacuum stuff.