Recurring question, no seeming answer...

[Xenn]

79 280zx engine in a 76 280z body

So I have searched the internet, and replaced most of my engine trying to solve a problem I cant seem to fix, a problem others have a variation of.

After a cold start, as part of the warm up systems, there is something that kicks in about 2 minutes after the car starts that is NOT the air regulator. Other people who have this problem it usually causes their car to die, or idle very low/poorly, it causes my car idles at about 2000 RPM. The problem is sudden, and takes about 20-30 seconds to take effect, but for others it is instant. Once my car is warm and has sat for about 20 minutes the problem goes away and it will idle correctly.

Vacuum is fine, everything in the thermostat has been replaced (including the thermostat) other than the water temp gauge, ner air regulator, connections have been cleaned etc.

My two thoughts are the ECU is haywire, or there is some valve that kicks in other than the air regulator at warmup and mine is shot.

It is related to heat somehow, taking longer to kick in on cold days, shorter of warm days. Always around that same 2 minute mark though.

My question to you is what cold start system kicks in about 2 minutes into warmup? Is it likely the ECU is doing this?

I have found a lot of people with this question, but never an answer, I hate to bug you guys but I am stumped.

[240260280z]

Bcdd?

[Zed Head]

Are you using the 1976 EFI system or 1979? They have significant differences. Also, 76 or 79 (or other) distributor? Which ignition module? 76 has two timing circuits, for example. And the 79 engine might have a few funky temperature actuated vacuum valves on the intake and thermostat housing.

I've actually never seen this problem described, with normal - high idle - normal. I've seen normal - low - normal, but not your scenario.

[Xenn]

BCCD is filled in, 76 EFI. 79 Distributor, alternator and ignition module. I have been upgrading it as I go, but the problem has persisted since I got the car running.

[Zed Head]

I would like for something that lets air past the throttle body or leaks un-metered air in to the manifold. It only takes a little at idle to get a lot of RPM. BCDD was worth a look. Check power to the AAR also. It should be on as soon as the engine starts, causing the internal heater to start closing the valve. Or you could pinch the AAR hose when the idle is high and see if it drops.

A few thoughts. If you can isolate it to one area you can focus.

I think that the EGR systems also have some temperature actuated devices. EGR is air in to the intake manifold. Supposed to be closed at idle but would cause an idle RPM increase if it opened. Are you running the 76 intake manifold or 79?

[Xenn]

im using the 79 air intake, and my AAR is new and seems to be working fine, even if it got no power the coolant would heat it up and close it.

I was thinking some heat activated valve on the throttle body possibly related to EGR.

I know the 76 TB have a valve or solenoid that physically adjusts the throttle during cold start to raise RPM, does the 79 have an internal one?

It acts like there is a valve that opens too far/gets stuck open and lets too much air in, and slowly closes when the car is off, but I cant tell if it is running lean or just revving high.

[Zed Head]

The 79 FSM says there's a valve, but it's on top of the intake manifold, not in the throttle body, connected to the coolant block (probably the one under the AAR). The thermal vacuum valve. Thermal and vacuum! Could be something. Connect to the throttle body by hoses. Might be worth a look, page EC-8. Maybe there's another port waiting to be blocked.

The coolant alone takes a really long time to heat up the AAR. I've had my AAR power disconnected and the high idle lasts forever.

[Xenn]

I have thought about that, it connects my i wanna say idle air valve (vacuum source) to my intake manifold via a tube that runs thought the BCCD (that I left unplugged) it has 2 plugs and screws in under my AAR, I am not sure how it functions/what its purpose is though. Does that seem likely?

[Zed Head]

The BCDD is full of passages, some of which enter the intake manifold. You could plug that line and see what happens.

[Xenn]

BCCD is filled in on the inside of the intake manifold, there are 3 openings in front of the TB, one connects the the vacuum advance and carbon canister, the other is the other I talked about earlier, and the big one in-between that goes to the BCCD, i filled In it because I suspected a long time ago that might be a problem, it helped other problems, not this one.

[Zed Head]

Well, back to your first post - I would focus on extra air, wherever it's coming from. The ECU can add or subtract fuel but without air there won't be a significant effect on RPM. And I would still pinch the AAR line to see if the idle drops when it's at 2000 RPM. Then you'll know for sure that the AAR is closed. The AAR itself might be new but the electrical system could be a problem. The AAR's internal heater is more important than the heating block underneath it.

[Xenn]

Ill pinch off the AAR just to make sure and play around with the TVV today and let you guys know tonight how those go.