92 Civic - Hesitate/stutter/stall when warm & below 2500rpm

I bought this civic (abused) over 4 years ago. Its an LX 1.5L. We've
been thru a lot together including a motor, computer, clutch, rad,
starter, etc. I've never taken it too a shop.
So now this issue has me stumped. One cold -15 C morning it started
up for 30 seconds and then stumbled until it died. I warmed it up in
my garage and have since narrowed down the symptoms:
Runs great until the engine is warm. As temp increases the problem
developes.
When hot and idling a quick twist of the throttle will cause it to die
over a few seconds. RPMs will increase normally if you twist the
throttle slowly.
When on the road, I can excellerate slowly until 2500 rpm. After that
I can punch the gas and rev to 5500 with no stumbling. Below 2500
under normal acceleration the engine cuts out until peddle is released
and then it revives. I can make it happen by tapping the gas, but
only below 2500 rpm.
I pulled a plug wire and ground a spare plug to watch what happened
when I caused a stall. Spark was great until the bitter end.
I have a recent fuel filter, O2 sensor, coolent temp sensor,
distributer assembly, and plugs.
No engine light, but computer gave me Code 3 (MAP) and Code 43 (fuel
delivery). I swapped MAPs with another Civic and no improvement.
After reseting computer, I can't get it to throw those codes again.
This problem is not intermittent. It is 100% predictable and was
obviously triggered by a very cold night.

I'm well into testing components. I've never checked vacuum and fuel
pressure, but this may be the time to get the equipment. Hoping there
is an obvious solution first.
Any ideas or input would be great.

 

Try a thorough purge of the cooling system. Follow the
manual's directions. Note that during the purge procedure
and in cold weather, it may take 30 minutes to an hour for
the radiator fan to come on twice.

Some engine control sensors will send the wrong signal, and
cause odd revving, if not fully immersed in coolant. Your
symptoms suggest this is the problem. But there are other
possible causes.

Also pour a bottle of Chevron Techron fuel system cleaner
into a near empty fuel tank, refill, and run.

 

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It could also be tight valves, but I'd agree there's AIR in the cooling
system. It's throwing out the idle speed and ignition timing. Fill the
reservoir to the MAX mark three days in a row and purge the remaining
air after.

'Curly'

 

in addition to the coolant and valve adjustment issue already
identified, consider replacing the distributor cap/rotor, plug leads,
and checking all the vacuum hoses.

dist caps can be tricky to diagnose because they can be ok cold, ok hot,
but in that short window where there can be internal condensation during
warm-up, they can lose you sparking power.

also, make sure the spark plug insulators are clean. sweaty fingers on
the insulator before fitting can leave conductive fingerprints.

read tegger.com and the section on electrical/starting problems.

 

I thought air in the cooling system affected idle more than anything.
My idle is fine. None the less, I will try purging the system.
I had a spare distributer assembly (including cap & rotor) when I
misdiagnosed the computer last year. The old one worked fine, and the
new one is a year old. Swapping them has no affect. Did the plugs
and wires also.
It feels like the issue is not ignition related.
What about fuel supply and mixture? What happens with a faulty fuel
pressure regulator?
Is it running rich or lean from idle to 2500 rpm? Since it's a quick
twist of the throttle that stalls it, could it be TPS sensor?
I think my fuel pump is OK since I can stomp the gas at 4000 rpm and
it goes fine.

I'll keep on it, but will be more productive this weekend.

 

You're right, this does sound a lot like what my car is doing. My
overflow tank was a bit low, so I topped it off. We'll see whether that
has any effect.

 

i've never got a similar experience, but i suspect a too advanced
ignition timing combined with a weak coil ( or weak ignition parts). i
would re-check the distributor assembly and the ignition coil

cheers