Can't get 1975 280z to idle

[Hutch]

New Guy here. Just bought my first Z. Ran fine when I drove it home. Had all the fluids dropped and had to tow the car home.Would run at a high idle 1200 to 1500 rpm,but when you put the gas down it would flood out.

Bought a FSM replace all vacuum hoses. Hook up everything that was not. Replaced thremo switch, temp sensor. Car runs but will not idle. The idle adjustment screw does nothing. It worked before I clean up the vacuum line mess. Any thoughts. Thanks.

[Zed Head]

Read your post. Maybe too concise. Statements don't tell enough.

Sounds like a vacuum leak or bad Air Regulator or both.

[FastWoman]

Do you mean it idles too high or idles too low now?

Could be the air regulator. Pull it off and look through it. You should see a half-moon shaped diaphram, as diagrammed in the FSM. Give it a wiggle with a small screwdriver to make certain it's not frozen in place.

Could be that the air flow meter is stuck. Check the metering vane to be certain it moves freely. Also try cleaning the electrical contacts inside the black box on the side. Careful, they're delicate!

Also check to see whether the AFM is damaged. The '75 model didn't have a backfire relief valve in the vane, so it was prone to damage. They fixed that problem in subsequent years, but I had a problem with my '75 many years ago. A hard backfire had apparently bent the vane, causing the engine to run rich. I carefully tapped it back into shape, leaning up the mixture considerably.

Obviously check that the air bypass port in your throttle body (where your idle adjustment screw is found) is not plugged. Be aware that it's not like adjusting idle on a carb. A fraction of a turn won't do much of anything. You'll be making your adjustment with even a few turns.

I just rebuilt the throttle body on my '78, and before I pulled it apart, I noted the position of the idle adjustment screw. It was 5 3/4 turns CCW from fully closed (screwed all the way in). Note that there is also a stop for the butterfly that would have a larger impact on idle speed, so my normal idle screw adjustment might be nowhere near what yours should be, but at least that 5 3/4 turns should get you somewhere in the ballpark.

Good luck!

[cozye]

Do you mean it idles too high or idles too low now?

Could be the air regulator. Pull it off and look through it. You should see a half-moon shaped diaphram, as diagrammed in the FSM. Give it a wiggle with a small screwdriver to make certain it's not frozen in place.

Could be that the air flow meter is stuck. Check the metering vane to be certain it moves freely. Also try cleaning the electrical contacts inside the black box on the side. Careful, they're delicate!

Also check to see whether the AFM is damaged. The '75 model didn't have a backfire relief valve in the vane, so it was prone to damage. They fixed that problem in subsequent years, but I had a problem with my '75 many years ago. A hard backfire had apparently bent the vane, causing the engine to run rich. I carefully tapped it back into shape, leaning up the mixture considerably.

Obviously check that the air bypass port in your throttle body (where your idle adjustment screw is found) is not plugged. Be aware that it's not like adjusting idle on a carb. A fraction of a turn won't do much of anything. You'll be making your adjustment with even a few turns.

I just rebuilt the throttle body on my '78, and before I pulled it apart, I noted the position of the idle adjustment screw. It was 5 3/4 turns CCW from fully closed (screwed all the way in). Note that there is also a stop for the butterfly that would have a larger impact on idle speed, so my normal idle screw adjustment might be nowhere near what yours should be, but at least that 5 3/4 turns should get you somewhere in the ballpark.

Good luck!

How'd you source the parts to rebuild the Throttle Body? Is there a kit available ?

Sorry for the threadjack.

[Hutch]

It Idles too low and will not adjust. I changed every vacuum line so do think that is the issue. Will check the air regulator again. Cleaned the AMF yesterday everything looked good.

Think I will pull the throttle body off and give it a good once over.

[webdawg1]

Might check all your connections using the following scanned image...might have hooked something up wrong perhaps...

webdawg1

[Zed Head]

A low idle seems odd. It should be easy to get more air in to the engine, raising the idle speed. What happens if you pull a vacuum line at idle? The idle speed should go up. At idle, the main one that goes to the carbon canister would be a good test. Even the little one that goes to the white vacuum jug should have an effect.

Maybe your throttle position switch (TPS) contact is not registering "idle" to the ECU, so you're not getting idle speed fuel enrichment. This might give a low idle due to lack of fuel. The TPS is easy to check with an ohm-meter or test light. This is just a guess.

[Hutch]

The tcvas was not hook up when I bought the car. When I replace all the vacuum hoses I hooked it up correctly placed a meter on it and it seemed to be in spec.

I also replaced all the vacuum hoses to the air conditioning too, from the firewall to all of the air conditioning components. Most of them where missing. Might go back and block off a few hose to see what kind of response it get.

[Zed Head]

I'm not sure what a "tcvas" is. If you mean TPS, then not hooked up is a bad thing. The TPS does not have any vacuum hoses connected to it.

Blocking a vacuum hose hose won't do much. Pulling the hose will let extra air in to the manifold, which should raise idle speed if there is fuel available.

On these EFI systems, all of the components are designed to work together. The ECU computer program takes input from all of them and adjusts fuel accordingly. There are only a few things that you can bypass or remove without messing things up. ... from my limited understanding in the short time I've worked on them.

[Hutch]

TCVS is the transmission controlled vacuum system. I can't see where that could be the issue but it's one thing that is different or was not hooked up.

[Zed Head]

Ah. You mean the 4th gear vacuum advance switch. Sorry for the misunderstanding.

That is an Emissions device that gives vacuum advance only in 4th gear. Kind of a weird thing. I disconnected mine from the switch and ran the hose directly to ported vacuum (basically just connected the two ends at the solenoid switch).

If you reconnected the electrical wires and all of the hoses then you will be running with no vacuum advance in gears 1 - 3. If the PO, for whatever reason, had connected your advance hose to a full time vacuum source, and set the timing that way, you will now have retarded timing, since the hose should be on ported vacuum. That would cause your idle to drop. Just a possibility.

It might be worth rechecking your timing with a light.

It's raining in Portland (where you're at too I see) so I'm spending too much time here. Tell me to stop if I'm overdoing it.

[Hutch]

Think I will delete 4th gear vacuum advance too.

Couldn't get the throttle body off. The bolt that was hardest to reach wouldn't let go. Hooked up the vacuum lines the way they were when I purchased the car. Same thing. Now I am getting a little backfire at low RPM's say 800 to 1200. Reset the idle adjustment screw to factory still nothing.

Haven't checked fuel pressure yet. I know it's running rich when cold because the wife asked why does it smell like that.