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Blue is correct to unplug the vacuum line from the FPR to see it it goes up to 36. If you can reach it but are having trouble maintaining 36 psi with return line un-crimped then you have either air in the lines or a flow rate problem. Even a slow flow will eventually get to right pressure if the engine is off or idling but once you are drive down the road that pressure will be difficult to maintain because the supply cannot keep up with the consumption. I replaced my pump thinking it was bad, only to find out shortly later my pump supply line had pin holes inside the tank. I would purge the air from the fuel line with a tank more than half full, and once the fuel level dropped below half tank the lines were not submerged in gas and started sucking air/fumes then the car would die. It was easy to see the air accumulate because I installed clear G3 filters on the supply side to catch all the sediment still in the tank. I'm not suggesting you have pin holes like I do, but a plugged filter, debris filled lines, air in the lines, or a weak pump would make it difficult to maintain pressure resulting in a lean condition.

@rcb280z, I will admit I didn't read the entire thread (and post 45 was quite a way back), really my post was an affirmation of a point made by FastWoman in post 87. Like I said I underestimated the impact of the AAR, until it was obvious it was the problem. Good to hear it's not related to your current state, I guess I felt a kindship at post 84-85 because I was there. I love my car, but it was not loving me. You may have already checked this in a previous post (maybe 45 which I will go read)...did you confirm with a multi-meter that closed throttle does close the idle contacts in the TPS? Meaning the TPS could be good, but the throttle plate is not returning to full close. Either the decel dashpot (assuming yours is manual) or the throttle plate set screw (not the idle air screw) being out of adjustment will prevent a full close. I'm guessing you already checked it. The CS130 upgrade on the 78 was very easy mostly because the stock alternator was also internally regulated, however I wouldn't expect it to be difficult in most cases since it's only needs 2 wires, and modified bracket. I anticipated needing more current because I'm field testing some driver performance electronics for my company. @Captian Obvious, Before resolution, I did think very much the same way you do, and considered the AAR negligible. Than a realization that hit me like a brick, and I changed my opinion. My AAR was stuck wide open, and to your point the AFM would open more due to the increased ingestion of AIR, and raise the fuel mixure....thus "in theory" making it no different that if your foot was on the pedal with throttle plate open. The part I was missing was that the TPS at this point is on the idle contact. Once I open the throttle any amount off the idle switch, the ECM generalizes (not like modern TPS with variable voltage) how much fuel is needed based on which contacts are made in the TPS. The ECM is expecting a margin of air flow based of the known airflow between idle and WOT switches across the throttle plate. The situation in my case was the volume of air was (expected position of throttle plate) + (1/2" dia full open AAR) = significantly more air volume than expected. Since the ECM doesn't have an o2 sensor, it wouldn't know it's getting more air than normal. Then with more air ingestion, the PO untighted the MAF spring to make the ECM enrichen the mix. This compounded the problem because they were both off spec, the MAF off by a ratio, and the ingestion off by (1/2 dia volume of air). Wouldn't the MAF compensate since it's measuring the amount of air flow? I would think so....but the reality is, the ECM attempts to reconcile the input of pedal position, and input readings from the MAF in precalculated "expected operating conditions" (meaning air filter clean, no vacuum leaks, AAR open the expected amount, injectors clean, fuel pressure good, etc) and the ECM get's decent precision data from the MAF, but only 3 states from the TPS (idle, non-idle, WOT). Given the disparity in precision between two components that need to be in operational agreement, there is little margin for the unexpeced. Unlike moderm FI systems that have variable TPS, o2 sensors, manifold pressure sensor to calulate and compensate for out of spec devices, leaks, and un-usual environmental conditions. So after all this I conluded that there is a signifianct difference between the AAR, and simply pressing the pedal. Pressing the pedal takes the ECM out of idle mode (which is intended to be a richer mix compared to non-idle). (page 13, 280z Electronic Fuel Injection, Theory & Troubleshooting) In my case, once the AAR was corrected every thing else could be adjusted as expected. For me the proof was in the results, everything worked, and my o2 sensor was reading a balanced mix after. **warning this is humor and not reccomended** To give you an idea how out of wack a wide open AAR will make your engine, try bypassing it....and plug the MAF Boot Hose directly to manifold port. The idle will shoot way up 3K+, and you will most likely not be able to accelerate with out stalling. **again do not do this** Despite my initial opinion that I was wasting my time cleaning and adjusting the AAR.........I'm now a believer the AAR can be very significant. The reason I'm glad I found the site (and shared it), because it is a "real world" guide that takes into account the realites of aging systems (In contrast to the Datsun FSM, which appropriatly was not intended to cover.

@grantf thanks for the advice, but it's disconnect at the moment @everyone I found out that running the headlights also induces a smoother idle.....so I feel confident that I'm dealing with an electrical conductivity issue, with either the ECM, the ignition system, for the Sense wire for the alternator. The alternator is charging at idle, but when high load accessories require the alternator to increase AMP's the engine electrical is benefiting from more available amps. In theory I believe the sense wire is the least likely problem, because if it had greater resistance due to corrosion it would register lower voltage to the alternator and it would begin over charging which isn't happening. I'm going to measure current draws of the ECM, injectors, and ignition to see which is benefiting most to the available current. It's also possible given the ECM is solid state and not digital, it can (in theory) be impacted by voltage swings. Fortunately if this is the case and not corrosion, I do have 12volt regulated power supplies I can add.

I just wanted to jump in because I recently had a very similar experience, where I was having a severe lean condition and rough idle on cold start and stall/sputter/intake backfire on acceleration during cold cycle. Although there were a number of contributing factors the main issues for me was the cold start air valve was sticking. I spent many a frustrating day adjusting the AFM, checking it with a multi-meter, comparing to another I had, swapping it out, without any substantive success. Additionally I continuity tested every sensor, and everything tested within spec. I was pulling my hair out in a troubleshooting session that seemed to go in circles. In the quick read of this thread you and I almost identically followed the same troubleshooting steps. Then I stumbled upon a very comprehensive “real world” L-tronic troubleshooting site, I found very helpful in truing up all the maladjustments from PO’s, and eventually revealing my root cause. http://www.hiperformancestore.com/Ljetronic.htm The entire doc is a good read, but the section “Step 4 The cold start and warm up system” maybe the most relevant to your present problem. I didn’t take the air valve that serious until I realized how much of a vacuum leak this is intended to create to support cold start, and how slow or sticking operation prolongs a lean condition. When I temporarily capped the line between the AFM boot and the Air Valve there was an immediate improvement. A remarkable difference was made for me when I cleaned and adjusted it (per the link provided). My Z went from un-drivable to drivable immediately. I still have a minor (very short) transition window near warm operation when the valve is still open a little too much, but it resolves in a very short time. I need to adjust it close a little more to get it perfect. A side note to the value of this guide, I realized how sensitive any air leak is for L-tronic, and as a consequence of following the guide I sealed up previously undetected leaks in the AFM->(Throttle plate boot), and a leak in my new PCV hose I ordered. I hope this helps

Thanks everyone for the ideas, and I apologize my signature didn’t post providing some basic information about the car. 1978 280z 4spd Stock FI (new injectors, new pump, new regulator) MSD 6A (stock Ignition Module removed) / Blaster Coil CS-130 alternator upgrade H4 HID's / MSA Type 3 Body Kit Honda Blower Motor Upgrade @everyone This Z is recently resurrected, and I’m still working through some of the aging issues. The last 3 weeks, I have been using it as a part time commuter car to surface issues. Currently the vacuum lines for the mag switches and vacuum actuator are disconnected because they were missing from PO’s and what tubing remained was degraded or misconnected. Since I have learned the hard lesson of vacuum leaks and lean condition with this FI, I’m incrementally testing all vacuum components and replacing tubing in stages. As it stands today the only (climate control) vac lines connected are Manifold->vac canister->cabin controls This minimal configuration was used to provide basic heat since the temp in GA dropped recently….prior to this all climate control vac lines were capped to troubleshoot a previous lean condition. I don’t hear the AC clutch engage, and I suspect there is not enough charge in the system to permit the pressure switch to allow current to the clutch . I will double check the AC clutch action this weekend. I suspect the problem to be electrical related (ground/load/ailing relay), because the odd behavior is immediate (where I would suspect a vacuum related issue would have a slight delay). With that being said, I do value field experience of forum users, and if this was a known quirk the best place to ask is here. I have had some interesting discoveries from PO’s “improvements” so at times on the surface it’s hard to discern what is a normal quirk, and what is unique to this Z. @black gold man It does have AC..looks factory @rcb280z Sorry for the missing info you should have it above…..normally it’s on bi-level or def….I only put it on bi-level because the coldest setting on heat is still too hot. Remember I leave the fan running when I drive to avoid the rough idle at stoplights I should verify if the behavior is repeatable for all control positions I don’t normally use. @SteveJ I did leak test the canister before connecting it, and replaced the vac lines with copper tubing. I admit the copper tubing for vac lines is overkill, but I’ve had my fill of vacuum induced lean conditions with this FI. @WilloughbyZ I do have the Honda Blower motor upgrade in place. I apologize for not mentioning that the AC components are largely disconnected (see above).

When the heater blower motor is not running the idle is a little rough......you turn the fan switch on high the idle smooths out. I suspect this is a grounding issue, power draw, or relay issue. I wanted to see if this is a known issue, before I begin troubleshooting. It's comically repeatable, and I would normally expect the opposite behavior. I have good charging regardless if the blower is running or not.