I posted about this a while ago. After it has warmed up the car will
not sit at idle. The revs cycle between about 1200 and 2000 every
second approx. Following suggestions here I drained the radiator and
refilled it with 50/50 coolant/water, and I inspected all the
hoses/lines looking for leaks. Everything looks fine. I also blasted
carb cleaner into the manifold. I have seen suggestions that I need to
inspect the O2 sensor and an idle control valve, but I don't know how to
locate these. The engine layout pictures I've located are from the US,
while this car was sold in Japan, 1.6L engine.
BTW, I'm having trouble finding out the designation of the engine in
this car (because it is a Jap import). It is definitely a Civic Si,
1.6L, DOHC, PGM-FI, and the NZ registration shows it as 1985. On the
tag in the engine compartment, among the Japanese characters I see:
The closest match I've found (Wikipedia) is the D16A3 engine, which was
in the 86-89 Acrua Integra, but the fuel control of this engine is OBD-0
MPFI, whatever that is.
I need to know the engine series ID in order to locate an engine
diagram, so I can find the IACV etc.
On Hondas sold in the U.S., the engine type is stamped on
the block, a little below and to the right (as you stand at
the front of the car, facing it) of the distributor housing.
You may have to wipe off old grease to see it. The letters
etc. are around an inch high.
The parts diagrams at bkhondaparts.com may help you find the
I've tried to locate the number stamped on the block, but it isn't
possible to see the block because the camshaft housing is wide (this is
DOHC) and there is hardly any clearance between it and the chassis at
Thanks, I'll have a look. I'm not even 100% sure that this engine has
an IACV, BTW.
Try also the free Factory Service manual linked at
http://www.honda.co.uk/car/owner/workshop.html , under PGM-FI
The 1985 Civic does not have an IACV nor EACV. The 88-92
have an EACV. The 93-95 have an IACV.
Thanks Elle, that's very useful, especially the service manual.
I have (fingers crossed) fixed the cycling idle problem. Following
advice I found online, I screwed down the plastic part inside the FITV
(fast idle thermo valve) and blasting carb cleaner through the small
throat within the main throttle throat (I'm not sure how to refer to
this - it houses the butterfly valve that is directly controlled by the
throttle cable). Now the idle speed is down to about 1000 when hot, a
bit excessive but I can live with it.
There is another problem that I have started to track down, possibly
related to the idle issue. The car runs fine but misses (stutters)
under load. If I accelerate moderately it goes up to motorway speed
without complaint, but under hard acceleration, or up a hill, there is a
lot of misfiring. I'll start by replacing the sparkplugs, then check
the sparks with a timing light. A question: I've seen the PCV mentioned
as a possible factor in misfiring under load. Do you know if the DOHC
ZC has a PCV?
BTW, in my defence, I haven't looked at this car for about 3 years. I
gave it my daughter to use, and she probably didn't want to bother me
with it. Now I have it back again, and want to get it in a fit state to
sell (which I will do reluctantly, because it's a great little car that
I inherited from my dad).
You saw in the service manual how to make an adjustment to
the idle, right?
Small caveat about the cooling system: After replacing the
coolant, one has to follow to the letter the instructions on
purging it of air. Where it says to make sure the fan comes
on twice, I learned the hard way this means letting the
engine idle for typically 40 minutes, even in summer
temperatures, until the fan does this. This is for my 91
I would not bet the problem is the PCV. OTOH, if it's never
been replaced, it's due. It's cheap enough.
It should. See for example
That's for the 85 CRX Si, which according to
http://www.superhonda.com/tech/honda_engine_codes.html , has
a ZC engine.
These old Civics cannot be beat. I keep an eye for buying
Over the years the wisdom on tuneups is to use strictly OEM
for wires, plugs, distributor cap, and rotor. It's amazing
how often a running problem is reported here and a new set
of wires fixes it. You sound experienced, so just saying for
The problem under load makes me suspect either the catalytic
converter (based on what others report here and reports on
the net) or the O2 sensor. Then again from checking
BKHondaparts.com, I am not sure your Honda came with a cat
If it's the original O2 sensor, consider a new OEM one from
www.automedicsupply.com. It should go for under $40. Even if
the old one still "works," they do degrade over time before
full failure. Might improve your fuel mileage. I have used
automedicsupply for an O2 sensor and was pleased with the
price, speed of shipment, and total cost.
A tuneup sounds very prudent, by the way. If nothing else,
it establishes a baseline so multiple problems are less
likely to confuse diagnosis. Plus a tuneup is due every so
often anyway, so it's not like money is being thrown away.
Thanks, I'll bear that in mind.
Something is screwed up with that bkhondaparts site. My Firefox says it
can't find the server. Google gives plenty of hits for bkhondaparts,
but I can't go to the sites.
I don't believe I have a cat converter.
I'll look at the O2 sensor after checking out the electrics.
Yes, I'm sure you're right. I have to overcome my suspicion of
Your engine is not from the car it it's in now. There is no 1985
Civic Si - I had one of the first ones in 1986. They have a
fuel-injected 1.5 litre 12 valve engine. Look for the engine (not
chasis) serial number. A dealer or mechanic can tell you which engine
you have from that.
I think you are probably referring to cars sold in the US. This was
sold in the Japanese domestic market, and imported used to NZ.
According to Wikipedia:
"Honda first adopted the Si badge for the JDM Civic in November of 1984.
Mainly offered in hatchback form (four-door Si's existed but were rare),
the main aesthetic difference was the slight bulge in the hood, which
accommodated for the 1.6-liter I4 DOHC engine. Designated as ZC in Japan
and D16A9 in Europe, the new engine put out 130 hp (97 kW). Since
compact cars at the time typically made less than 100 hp (70 kW), the Si
proved popular amongst tuning enthusiasts.
The United States saw the release of the Civic CRX Si in 1985 with the
Civic Si following in 1986, replacing the Civic 1500S-which shared the
non-fuel injected 1.5 engine as the rest of the Civic lineup. The trim
of the Civic Si was geared toward those who wanted the performance of
the CRX Si, but with four-seats. Standard equipment for the Civic Si
hatchback included a removable glass moonroof, tilt steering wheel, a
full-width taillight panel and color-keyed front airdam and roof spoiler.
Unlike the JDM Si, which had a 130 hp (97 kW) ZC engine, the USDM Si
featured a 1.5-liter, 91 hp (68 kW), 12-valve SOHC engine designated
EW4/D15A3 (the latter code was used for 1987 but with same specs). 
The Civic Si also saw a release in New Zealand and Australia in 1987,
and sharing similar specs to the USDM Si."
The ZC number I gave is presumably the engine number, consistent with
other info I've managed to dig out. The engine seems to get referred to
as the ZC DOHC 1.6L. The problem is that although it's easy to get info
about the models sold in the US, this is not true for those sold only in
Japan. I suspect that something similar was sold in Europe, but I don't
know the model name. BTW, the markings on the back of my car say Civic
Si Aerodeck, but Aerodeck usually refers to an Accord model. Mine is a
3-door with a very similar shape to Accord Aerodeck pics I've seen, but
not so long I think.
I stand corrected - I passed over your mention of it being a
Japanese import, or misunderstood...anyway, what Elle wrote about
looking for the engine serial number as stamped on the block, is your
best bet. That will give you the specific engine type.
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