That could be the BCDD, either out of adjustment or bad.  Could be the dashpot?  Or the fuel tank is clogged up.  Have you put a Fram G3 clear filter coming out of the tank?

BCDD instructions.  Mine went to a high RPM when I came to a stop but yours maybe the opposite?  

Anti-stall dashpot shoots a rod out and catches a throttle linkage flat to keep them from doing what yours is doing when you let off the pedal.  You'll have to look at it and see for yourself how it works (or doesn't).  Google "280z dashpot" for more info, I can't find anything other than they only come on manual transmission cars.

Fram filter instructions, http://atlanticz.ca/zclub/techtips/fuel/g3filter/index.htm

Edited January 2, 20178 yr by siteunseen

Another thing that affects idle is the TPS.  http://atlanticz.ca/zclub/techtips/tps/index.html

Do you buy good gasoline? Could there be water in the tank? Do you buy fuel at a busy gas station? The busier the station the more they change their inventory and the less water they will have in their fuel...

The dash pot is easy to adjust, just loosen the big lock nut on the top and turn the whole thing in.  Watch the tach needle to see if adjustment will help.  If the needle drops like a rock and bounces off 500 or so before rising up to your set point then an adjustment will probably help.  If it drops slowly to the set point it's already good.

If you have your idle speed set too low you can get dying when the engine is cold also.  Try raising idle speed 100 RPM.  The fuel pump control relay looks at alternator charging and oil pressure, both affected by idle speed.  It's bypassed at Start.  

Thanks for your replies. I dont think it is my dashpot or BCCD, my dashpot is disconnected, and ive driven with a bad BCCD, i can cover and test the BCCD though.

As per ZedHead, i upped the idle speed, i only use good gas, premium from a busy gas station. I have a prefilter coming out of my gastank before the pump that is clean. Ive replaced the TPS and adjusted it.

The fuel pump is wired directly into my fuse box, it bypasses the relay.

I kinda think ZedHead was right from awhile ago, I think something is heating up and cutting out signal from my tach to my ECU or vice versa. I only have issues when the car is up to temperature. Never when cold.

People have had issues with fuel pumps that overheat.  I had one (just a tester in the garage) and FastWoman had one, in her daily driver.  Took her quite a while to figure it out.  The pump can be turning, just not fast enough to generate pressure.  So you'll hear it but pressure will still drop.

Leaving a gauge on the system while you have the problem will offer a clue.

2 hours ago, Zed Head said:

People have had issues with fuel pumps that overheat.  I had one (just a tester in the garage) and FastWoman had one, in her daily driver.  Took her quite a while to figure it out.  The pump can be turning, just not fast enough to generate pressure.  So you'll hear it but pressure will still drop.

Leaving a gauge on the system while you have the problem will offer a clue.

I had one but it died, i guess its time to buy an expensive nicer one.

So since my fuel pump was new probably 5 years ago and has been through some tough times i ordered a gsl392 fuel pump to replace my current one (which was annoyingly loud as well), it should be here this weekend.

The noise could be from a clogged inlet filter.  They don't like to pull.

Edit - by the way, that 392 pump is waaayyy over spec'ed for the L28.  670 horsepower?  50 gallons/hr at 80 psi?  Not gonna get there, not necessary.

http://walbrofuelpumps.com/walbro-gsl392-inline-fuel-255lph-pump.html

Edited January 3, 20178 yr by Zed Head

Yeah i know its overkill, basically i want it to either 1 not have to work hard to get the job done and thus be more likely continue working in less than ideal conditions (as well as hopefully be quieter), or 2 excaserbate whatever problem there actually is (rubber flap in the lines, clogged inlet) to make it eaiser to diagnose. ive blown out the lines both ways with air, but you never know if there is a problem still hiding. Its also too cold to drop the tank or rip out the lines, so if it is something like that im going to need to wait a month or two to fix it.

I think Zed Head was mostly right, it happened again today but i was close enough to work to make it into a spot where I could look at my car, i was trying to find anything that seemed wrong or out of place, and i realized my fuel rail was making a "tist tist tist" sound like it was trying to pump air mixed in the gas, the lines were cold so its not vapor lock. After sitting for a few minutes this went away. Im thinking the o-ring on my pump may be shot, and as it heats up it starts to suck in more air. Ill find out when my new pump arrives, sadly this is just an educated guess, my free money this paycheck went to a new pump rather than a new FP gauge, if the problem persists that will be my next buy.

The sound was probably not air (but might have been) but just the gas squeezing past the internal valve in the FPR like it's supposed to.  But usually it's just a steady "ssssss" noise.  When my garage pump started to lose pressure you could hear the rotation of the motor starting to stall like it was binding up.  So the noise is a clue.

There's no o-ring to leak, at or in the pump, though.  It's just a hose on a tubular fitting or barb, and a tight clearance metal roller assembly inside the pump.  

Here's one thing that comes to mind though - a hole in the tank's pickup tube.  This would cause air sucking when the fuel level got low.  I can't remember if you mentioned fuel level but you might watch and see if the problem only happens at low fuel levels.  Fill up and see if it goes away.