76 Datsun 280z throttle sticking

[TomoHawk]

On 10/14/2006 at 2:32 PM, KDMatt said:

the yellow-bottle (which used to be clear...ish) is a vacuum container as far as I know, and is hooked up to the inside of your car. I think this is what allows you to switch from the vents on your dash to your defrost vents... if this isn't hooked up it could spell fog trouble the next time it rains,

That bottle is just a vacum reservoir, which stores some vacuum so you can change the vent function while you are at low revs or low vacuum.

[TomoHawk]

In my case, the sticking is in the large torsion bar bearing on the firewall.  I  don't think it can be disassembled, polished,  or repaired.

[Zed Head]

Necro posto...  He hasn't been on the site since 2008.

I found that what felt like sticking was actually the bell crank being adjusted, or out of adjustment, so that the starting point was "over center".  You had to apply extra force to the pedal to get it over the top then it would gain leverage and get easier, making it feel like it had been stuck.  You can lengthen or shorten most of the little arms of the linkage to fix that problem.

 

 

[TomoHawk]

I don't feel any resistance when pressing on the throttle pedal.  In stead, when you press a bit on the throttle, like if you were just trying to get the car to roll forward slowly,  the throttle would stay where you had it, like a sort of high-idle.  Giving it a little blip will allow it to settle down  to the 800 RPM.

I looked into the bearing, and it gets cocked in the seat, so I think that's what is happening- you press on the throttle, the looseness on the bearing allows it to get cocked, and it stays where it is. 

I don't think you can disassemble that part.  It should have been designed better, with a sealed bearing instead of a ball-and-socket arrangement.

 

Edited August 10, 2018 by TomoHawk

[Zed Head]

Could be a gummed up throttle body blade.  Nissan rerouted the PCV hoses to combat that.

[240260280]

I had to move that part above when putting SU's on my 280z.  Only the two outside 3 holes are used on the 280z.  The unused middle hole aligns perfectly with the left most captive nut  the when moving the part to align with the SU intake.

 

[Captain Obvious]

I fought a sticky throttle body causing a handing idle for quite some time. Here's some of my (mis)adventures:
https://www.classiczcars.com/forums/topic/45152-sticky-throttle-body-hanging-idle/

I even modified my throttle body to include delrin bushings instead of the original worn steel bushings"
https://www.classiczcars.com/forums/topic/57126-sticky-throttle-body-fix-delrin-bushings/

None of that worked. In fact, my Delrin bushings were even grabbier than the stock steel and made matters worse. Worked fine when cold, but caused significant troubles once everything got hot and expanded. That project was a complete failure.

I finally gave up and switched over to a completely different throttle body from another car, and it's awesome. I've been meaning to post up details. but haven't had the chance. I will do that soon.

[siteunseen]

On 8/10/2018 at 6:04 PM, Zed Head said:

Could be a gummed up throttle body blade.  Nissan rerouted the PCV hoses to combat that.

That's what caused my hanging high RPM.  Cleaned the throat with lacquer thinner and an old toothbrush then rerouted the PCV hoses like the '78s.  Works good now.

 

 

[Zed Head]

On 10/13/2006 at 7:15 PM, 76Datsun280z said:

. After taking the engine to a machine shop, we found out that the engine was a l24 engine with the l28 fuel injection system on it!! As I'm sure you guys are aware, the l24 heads weren't designed this way at all.

After a few phone calls, we tracked down a l28 engine with nothing on it, we would just swap the fuel injection system and exhaust maniflold on it that we already had.

Except when it's cold, it runs very very rich and very rough, and that's something that I'm going to ask later on but one thing at a time I guess.

the throttle started getting stuck at around 1800-2000rpm. I'm always noticing this when I come up to a stop light or basically when ever I stop. I just kick it down and I'm on my way, but I'd like to get this taken care of. For some reason when I'm playing with the throttle in the driveway, it won't get stuck! I'ts only when I'm driving it that it gets stuck, I don't know why.

On the sticking throttle, one thing about the gummed up throttle blade is that it only happened when the engine got warm.  Which might fit your symptoms.  If by "kick it down" you mean pull it up with your toe, then that's a sign.

Nissan did make a fuel injected L24 engine.  The L24E, used in the Maximas.  Could be what you had.  Might also be that you had an L24 with an L28E head.  Check the head markings for that.  N42, N47, P79, P90.  The Maxima L24E had an N47 head but it had a CHTS, which the 280Z N47 head did not have.  That's how you tell them apart.

Running rich cold but not hot is kind of odd.  Usually they just run rich all the time.  Good luck.

[TomoHawk]

It was the carpet, bunching up in the corner next to the throttle pedal.  I took off the little connection rods to find where it was sticking.  The plastic bushings were 'gunked up' a little, but didn't 'stick.'  I can smooth the carpet out, but it bunches up again after a while from your foot making the carpet move around while you drive.  The plastic protector bit  next to the throttle pedal just won't lay flat-  can you smooth it out with some heat maybe?  Maybe I can get some Velcro on the transmission tunnel to keep the carpet in place, or maybe the padding underneath  needs some work.

Bruce-  Can you just tell us the source of your awesome throttle body?

Edited August 17, 2018 by TomoHawk

[Captain Obvious]

The throttle body I've been working with is (basically) from a 96-98 Sentra. There are some differences between the beginning and end of that range. Most noticeably the inclusion or lack of a vacuum port for the distributor advance. The earlier ones (96) have the port, but they stopped using the port in 97. Presumably digitally controlled instead of vacuum starting in 97.

It's not a direct drop-in swap, but it's manageable. I had to make some customizations, but here's a teaser:

One thing to note on the above pic is the green spring in the lower left of the Sentra throttle body. That spring is part of a system that boosts the idle when cold by acting on the throttle linkage. It's essentially the same function performed by the AAR system on the 280Z. Using the throttle body above allowed me to completely remove the AAR system and all it's associated plumbing while still having a boosted idle when the engine was cold. The tradeoff is that you have to plumb the new throttle body with coolant to heat up the built-in thermostat.

If you don't mind keeping the original AAR idle boosting system, then here's another option... I didn't buy one and dissect it in my shop, but just from analyzing at the yard, I believe the throttle body from an earlier Sentra would be a pretty easy adaption as well. This is from 94, but I don't know the year range. It's simpler than the 96-98 version as it does not have the temperature controlled idle boost incorporated into the linkage. I chose the 96-98 version because the temperature controlled idle boost allowed me to get rid of the whole AAR system and still have a boosted cold idle. Note that this one has the vacuum port connection for the distributor:

[TomoHawk]

Thanks.

Unfortunately, the cylinder head on something like the L28 is more-or-less perfectly-designed for street use.  To make use of a large-bore throttle, you'd need a cylinder head with larger combustion chambers and valves, larger ports, larger intake runners, ad a larger plenum.  There is someone on CZCC that has constructed a successful twin-cam cylinder head, but that's all I've heard of it.

It's too bad the cylinder head is about the only part that doesn't have a modern substitute, like the 4LN71 or 300ZX  transmissions and the Hellfire EFI.