so, i been driving this civic for a while now with no issues.. 87 civic wagon with 5 speed and 3 barrel carb.



recently it has developed this weird idle problem. sometimes it will die at stop light... or will rev to 2,000 rpm and everything in between. and it used to (when cold) start fine and slowly rev up to high idle and sit there for a few minutes then hear a click and would instantly drop to normal idle.

it no longer does that, it will die instantly if i take foot off gas and idle is everywhere.

i thought maybe was a vacuum leak and so far i have replaced 18' of vacuum line and the carb base plate... still no luck. i believe it has something to the high idle circuit not working right. also... i checked and replaced plugs.. they were white! very lean i suspect, which is most likely a vacuum leak.

i have sprayed round intake while running and idle doesn't change, so i think that gasket is ok.

any ideas?

 

The carb models are a real nightmare. I think this has the system that is basically an intentional air leak to lean out the idle according to readings from the O2 sensor. You could try blocking the hose from the valves in the black box to disable it.

 

yes it is a nightmare.... i have never seen anything quite like it. i took a black box apart (on firewall) and replaced all the vacuum lines. sadly, after spending the whole afternoon doing that i didn't find a bad one (tested each one with hand pump).

gimme a lil more info on the black box you are talking about. where is it located and whats it look like.

i will try anything at this point, can't figure this one out.. the amount of vacuum line on this thing is nuts.

thanks for help...

 

I think the mixture control box is on the left fender-- it is not the one near the firewall. There are two funky valves inside the box and one has a relatively large hose back to the manifold. Pinch off that hose and see if it runs better.

 

will check that out... thanks. when you say left.. i assume you are standing in front looking at engine bay. so you mean passenger side, correct?

 

had a look see, but never really found that valve you were talkin about. then was gone all weekend doing a dual sport ride in ohio. got home and had another look around... still couldn't find it. so i just got to pinching off vacuum lines with a pair of needle nose vice grips. and when i pinched off #26 from the main box on fire wall... the idle dropped a bit and smoothed out to normal. i drove it a bit and seemed to work as it should. i am sure this didn't fix anything... but certainly has helped. now i need to find out what vacuum line #26 does because now i have disabled whatever it was responsible for. but for now... it is better.

anyone have any idea what vacuum line #26 does?