Probably not too far from Captain Obvious

@siteunseen I thought the same regarding the throttle blade but it doesn’t stick, at least when it’s cold. When i manually press the throttle and let go, it goes back to the neutral position. The only slight play is in the linkage and that doesn’t actually move the blade. I will say, the holding rpms does happen more after the car warms up. Probably takes about 15-20 mins after driving that I really start to notice it.

@Patcon idk where he is but i recall seeing he was in PA in one of his posts. @Captain Obvious where you at in PA?

If you can blip the throttle and the idle returns to where it belongs, then the issue has nothing to do with the BCDD. That kind of hanging idle is a mechanical issue either with the linkage, or with the throttle body itself. I had that problem with my 77 and after lots of investigation and changes, the only thing that fixed it was to switch to a completely different throttle body.

I ended up adapting a Sentra throttle body and adding a cable linkage. Bunch of work, but it's smooth as silk now.

And I'm near Philly. Lancaster is about an hour and a half from me. Depends on the traffic (which is often terrible for some unexplained reason!)

Here's some reading that might help.

https://www.classiczcars.com/forums/topic/21910-76-datsun-280z-throttle-sticking/page/2/
https://www.classiczcars.com/forums/topic/45152-sticky-throttle-body-hanging-idle/
https://www.classiczcars.com/forums/topic/57126-sticky-throttle-body-fix-delrin-bushings/

On 6/5/2026 at 9:56 PM, dar5052 said:

I could recreate the high idle by just pushing on the throttle linkage under the hood. When I let go, it would hold a high idle. Then I would literally pull back on the linkage ever so slightly and the rpm’s would drop.

Is the other throttle return spring attached?

Me again. Never thought I'd hang around this long. Just lucky that I bought a car with all of the problems.

Edit - p.s. - check the linkage back to the firewall and to the pedal in the cabin also. Might need lubrication or adjustment. Don't forget carpet under the pedal.

Edited June 8Jun 8 by Zed Head

Thanks @Captain Obvious your symptoms sound exactly like mine. I’ll shift my focus away from the BCDD for now. I think I have a couple spare throttle bodies laying around so maybe I’ll try to clean one up and swap it in.

@Zed Head yes, I have the springs there. One helical on the throttle blade shaft and the second one drops down under the throttle body and attaches to a bracket.

I finally got around to taking things apart and taking a closer look as to what might be causing the issue. The inside of the throttle body did have some gunk in there and I assume when things heated up and expanded, it was probably just enough to bind the flaps from fully closing. I had a spare throttle body laying around so I cleaned that up really well and now ready to throw it back in the car. The replacement TB is from a non-egr so one less port to plug but while comparing the two, I noticed a really small adjustment screw on my old (egr) TB kind of close to the egr port. Any idea what that’s for?

While I was here, I decided to check some other things and found that my air regulator is fried. It was stuck shut so it wouldn’t explain the holding rpm’s but does explain why it would always limp along until it got up to temp. Luckily I have a few spares of those too that are hopefully functional.

Lastly, where the linkage from the firewall hooks onto the linkage on the throttle body, the hold down spring was missing… I found one in my bolts bin and fit it up. Hopefully the combination of these things clears up the issue 🤞.

So it seems that cleaning everything up worked…. But now I have another issue. I was intermittently getting a really hard brake pedal but now it’s just constantly hard to press down and barely stops the car. I’m thinking it’s the master vac because when the issue became constant, I noticed the idle was pretty bad on the car too. When I remove the vac hose from the booster, the idle doesn’t get much worse but when I put my finger over the check valve, it improves. So it seems like a master vac issue. Any other ideas before I go buy a new one?

Edited August 22Aug 22 by dar5052

By chance did you remove the check valve and re-install it. Reason I ask is I had mine in backwards and the symptoms are the same you’re experiencing.

Thanks for the suggestion @Yarb . I did verify that the check valve is functioning and facing the correct way (arrow towards intake manifold). I ended up pulling the master vac out and took it apart. Found 4 or so tears in the rubber diaphragm, most were between 1/4 to 1/2”. Quite frankly, I expected it to be worse but I guess even a small few tears will prevent it from building vacuum. I ordered a new one so I’ll get that installed and see if that improves the situation.

I doubt it would build vacuum with just one 1/4" tear

@Patcon I agree that a 1/4” tear is sucking some air but I highly doubt all the tears happened simultaneously so it presumably was building vacuum. Not saying it’s ideal by any means and it should be replaced, but it does build some vacuum, at least enough to be functional. Most of the tears were in the crease so it’s possible they were holding pressure just due to the location of the tears but eventually one of them must have propagated and just gave out? Idk, just speculating… but the fact that everything happened simultaneously (shitty idle, non functioning brakes, rpm spikes) leads me to believe this is certainly the culprit. I’ll revert back when I install the replacement but I’m off to Oklahoma tomorrow for work so it may be a couple weeks…

I appreciate everyone’s feedback and commentary. Always good to talk about these issues with members with these, or similar, cars.