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my 97 civic with a d16y7 runs perfectly then randomly stalls, mostly while idling at a light but a few times as me or my wife were driving. no pattern with stalling some times it wont stall at all other times its relatively frequent

heres some helpful info:

117K miles

oil pressure:
80-85 psi on a cold start
14 psi warm at idle
72 psi warm @3000rpm
thats within spec and good, oil pressure switch was just replaced and oil pick up was checked and it was clean. oil was checked a couple of times over two days

fuel pressure:
36 psi at idle and primes immediately

ign coil:
primary .9ohm
secondary 16.2 ohm

-no trouble codes live or stored
-checked over the engine cant find any vacuum leaks
-dist cap points look good, wires are good plugs are good rotor is clean and looks good
-battery was just replaced with new
-alternator was replaced with duralast remanufactured (see picture for its health but im some what questioning if it was a dud, lifetime warranty so i could replace with another for free)
-starter was just replaced (separate grinding issue fixed now)
-idle is ~650 and within spec when its running like usual
-new battery terminals, and grounds seem good
-when it runs good it sounds perfect no reason to suspect compression, doesnt burnoil has no knocks

notice when it stalls at least once the battery drops to ~7v which is weird and when putting a full load on the electronics (lights brights ac radio brakes etc, when parked) i was able to see the voltage dropped way down when measured right at the battery

but when it was driving fine it was charging fine considering the ELD hondas run and that the voltage shown was from the obd2 port it was still 12.3v+ so that should be enough to keep it running (its above 12.5V when measured directly at the battery not the port)


im thinking next i could clean the iacv?

any help or leads to check would be appreciated

thanks for the help

 
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quick update, didnt pull off the throttle body or iacv yet but i did the iacv tests in the manual, fully warmed up fans came on dropped the throttle back to idle and unplugged the iacv and the rpm's did increase from about 650 to 1300 turned the motor off and did the ohms test on the connector its a 3 wire with neg lead in the middle and pos on either side i had 18.5 ohms on the right and 18.6 ohms on the left so according to the manual the iacv should be ok but im sure cleaning it wouldnt hurt same with the throttle body/plate

went back to looking for vacuum leaks so far no luck, brake booster vacuum line was a little loose and easy to spin on the manifold side so i put a new clamp on there but no real change

 
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i went ahead and ordered a smoke machine, ill be better able to check for vacuum leaks maybe i missed something

i see other threads where people talk about increasing the idle but im hesitant to do that since when it runs it runs perfect and is perfectly within spec

 
Rep Power: 221

I wouldn't personally mess with the idle. Unfortunately I don't have any other suggestions, unless when the battery voltage drops that shuts the car off. So maybe charging/battery issues

 
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yeah im not going to mess with the idle, im just waiting on the smoke machine at this point and if i dont find anything i might just clean the iacv and throttle body since it wouldnt hurt anything and itwould eliminate them as problems even though the iacv has already passed the manual tests

ive also thought about battery/charging but both the battery and alt are new, i guess its possible the new alt was bad but i do get 14+v charging but im not sure why it dropped to 7v the second time it died on the screenshot

 
Rep Power: 221

These cars are very picky when it comes to electronics (sensors, alternator, etc)

 
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ill keep that in mind ive never had an issue with this car until the oil switch went bad and the alt was replaced, if i dont show any vacuum leaks and cleaning the iacv doesnt help than maybe ill just replace the alt since its free and it was a remanufactured it could have been a dud ive seen it happen before

 
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just did the smoke test and i found no leaks...ill do it again later when its dark out maybe that will help, but assuming there are non which is a good thing im back to square 1

im hesitant to pull tb or iacv because i have no reason to think theres a tb gasket leak and when i did the iacv tests everything worked as it should.. but a cleaning wouldnt hurt anything so i might do it just as preventative maintenance

 
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ok re did the smoke test at night, my wife helped so i had an extra set of eyes and found no leaks, tried the brake booster and the manifold and nothing which isnt a bad thing but i still cant find a reason for the random low idle then stall

points wernt terrible but showed signs of wear so i might replace cap and rotor with oem and replace the plugs, for my records i might do a compression test even though i know the compression is fine

i hooked up a timing light and everything looked right but i also didnt think there was a timing issue, and the valves sound good but i haven checked the clearances yet so i guess i can for the heck of it to check them off the list

any other thoughts of what to check?

 
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If you’re confident you have sufficient oil pressure, I would jumper the oil switch to ground and drive around. This would confirm if new oil switch is chattering.

 
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i tested the oil pressure over two days four times twice in the morning and twice at night each time i got the same results which were listed above and all in spec so im confident the pressure is good and it is a new oil pressure switch, i guess it could have been a dud but it is from honda not an aftermarket so i feel pretty good about that and it stopped the oil light from coming on like it was doing even though the pressure is/was good, it is possible though that the connection isnt the best ill check that, but could a bad connection cause a stall?

i thought the oil pressure switch was more of a dud warning light? the switch its self doesnt measure pressure just whether it has too little/none/less than 10psi from what ive heard. does the computer use it as a cut off switch if your pressure is too low?

either way when i get a chance ill double check the connection and do as you recommended and ground it to see if that has an effect

 
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i also saw someone else whose idle issues improved after replacing grounds with 4awg and freshly sanding mounting spots to clean bare metal. im about to go to fl for my wedding but when i get back im planning on improving and cleaning the grounds since it cant do anything but help, ill probably do 4awg on the positive side as well to make sure everything is fresh clean and as good as it can be

 
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To get downs to basics, I would check and record compression psi. I know you think it’s good. Check anyways. Check spark plug electrodes.
Then, move onto fuel delivery. I’ve seen lots of dirt in gas tanks. Change fuel filter.
Last thing left is ignition.

 
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sorry for the delayed reply i went to fl for a week for my wedding but ever since my last post it just stopped stalling or idling super low... i didnt check compression but i checked everything else again but i cant find anything wrong and it just stopped its issues.

ill probably check compression soon when i replace the plugs and ill upgrade the ground and clean the grounds contact spots but weirdly it just stopped stalling and its been daily driving again for a little. but im not complaining since it runs perfectly again

 
Rep Power: 221

Maybe just some bad gas?

 
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yeah i guess it could have been bad gas, but it seems to be good now its being daily driven by my wife and shes not mentioning any issues and it doesnt happen when im driving it so idk but im not complaining haha