Hi. The idle problem on my 85 Si 1.6L (sold in Japan) has gone from intermittent to constant. Once the engine has warmed up the idle speed goes into a cycling pattern, between about 1200 and about 2000 rpm every second or so. This also happens at low revs while driving, making the car undriveable.

I do not have a manual for this car. I have replaced the coolant (50/50) because I saw a suggestion that it could be an issue of the coolant temperature not getting high enough. I've also looked for leaking hoses etc., but everything looks OK. I've also seen mention of the O2 sensor, and the idle control valve, but I'm not sure where these are. Does anyone recognize these symptoms?

Thanks in advance.

 

First, get the manual here:

http://hondatech.info/downloads/Auto/Manuals/Civic/

Second, have you checked the self diagnosis system (see pictures)?

See additional pictures for troubleshooting charts.

 

Hi. I have seen those manuals, but it isn't clear where my car fits in. The ECU seems to have one light only, which is giving 5 flashes, which might mean a MAP sensor problem - but where is the MAP sensor? This car was sold in Japan, and doesn't seem to correspond to any US model. I've seen it referred to as the ZC engine (DOHC, PGM-FI, 1.6L). I found that the hot water flow through the FITV was blocked by corrosion in the pipe. Cleaning that has pretty much fixed the idle problem, but there is still a problem with how the car runs. The idle is a bit rough, and the engine misfires under load, to the point of stopping firing completely when the throttle is opened wide.

I'd be interested if someone can tell me what the engine code is. I suspect it is one of D16A1, A3, A8 or A9.

Also I need to find out how to seset the ECU, to make sure that the error code is flagging a real problem, and not just remembering something silly I did.

 

Code 5 seems universally to indicate a MAP sensor problem, and the symptoms you are experiencing fit with this idea.

Here's how to locate the MAP sensor:

The MAP sensor has a 3P electrical connector and is also attached to a vacuum hose coming from the throttle body. My guess would be that there is a leak somewhere in the vacuum hose or its connections or that the MAP sensor is bad.

 

You could try a couple little tests; try unplugging the O2 sensor and see how your car idles without it. You should find it next to the injector. Or, remove the fuse for your injector (inside the car) and see if you still have the problem.

 

Thanks Ron, I'll try to track down the MAP sensor circuit.

Note that the engine codes in the list you posted don't include a 1600 - this car wasn't a 1985 Civic in the US.

Thinking about it last night, it occurred to me that by following some online advice about the FITV I might have created a problem for myself. I could have fixed the FITV problem simply by cleaning out the blockage in the coolant pipe, but unfortunately before I removed it and discovered this I had already screwed the plastic air-valve part down, having seen the advice that this was the way to fix the cycling idle speed problem. Now, of course, I don't know where it should be set, and I suspect that this might be important for more than the idle. As far as I can see this engine doesn't use an IACV. If this valve isn't adjusted correctly it will not be possible to adjust the idle screw correctly, right?

 

OK, I'll see if I can locate the O2 sensor. Regarding the fuse, the hitch is that almost all the writing on this car is in Japanese. As I recall in the fuse box the only fuses with non-Japanese labelling are the ECU fuses (yes, there are two). I guess I need to get a Japanese friend.

 

I understand that the US and Japanese Civics are not identical, but I am hoping they have enough similarities that the US information helps to lead you to a fix.

I recommend that you focus your main effort addressing the code 5 fault.

Does any of this information help?

 

The engine and chassis numbers are on a blue tag at the front right of the engine compartment, by the battery (where the picture shows C MODEL).
Chassis: AT 1024071
Engine: ZC 1032126

 

Problem solved! My mistake! I had taken off the throttle body for checking and cleaning, and to get better access to the FITV, and very stupidly forgot to reconnect one little hose when I reassembled it. I just noticed it while poking around trying to find the MAP sensor (incidentally, there does not seem to be any device on or near the IM fitting your description, with both an air hose and an electrical hook-up). I reconnected the little hose, on the back of the TB just next to the FITV, disconnected the battery for a while, and the light on the ECU stopped flashing.

I have tentatively adjusted the FITV and idle screw, based on my rough memory. The FITV part I screwed in almost to closed, so there is still some suction with the engine hot, but not much, then I adjusted the idle screw to give about 800 rpm hot. Now it purrs like a ***** cat, but growls like a tiger on the motorway. No missfiring! All seems as good as new, but I might still take it to someone who knows what he's doing for a tune-up.

BTW I think I located the O2 sensor, but I can't remove the two screws holding it on. Rather than graunch them I decided to leave it alone.

Thanks to Ron (and Daeva) for help. This is a very useful site.