Caroline wrote:
> "Chopface" <thename_is_slick@yahoo.com> wrote
> > I've got a '91 Civic Si with the stock 1.6L MPFI setup and a manual
>
>>tranny. I put an AEM cold air intake on in August and I don't suspect
>>any problems from it directly. It has 136k miles and is well maintained
>>as of late (IMHO).
>>
>>Over the past few days the car has developed an idle problem. I have no
>>check engine light indication. The ambient air temp. has been around
>>30-40 deg. F lately. The fast idle seems normal when I start the car,
>>but after I have driven the car up to operating temp. (either cruising
>>on hwy. or around town) the idle bounces repeatedly from 750 - 1250 rpm
>>in neutral with the clutch out. I also seem to be getting lower gas
>>mileage (low 30's vs high 30's).
>>
>>I changed my coolant this summer, and never bled the system. I just
>>squished my upper rad. hose a bunch after filling it up and running it.
>
>
> I think I learned the somewhat-hard way that bleeding must be taken very
> seriously, or air pockets and so inadequate cooling results around vital
> components like the Idle Air Control valve (a.k.a. EACV).
>
> I'd just add that it will likely take at least 40 minutes to get the
> radiator fan to come on the first time (which the manual says to do when
> bleeding) and so do a thorough, proper purge.
>
> I did a bleed this summer, and the ambient temperature was 79 degrees F.
> Forty minutes is about how long it took for the fan to kick on. One is
> supposed to let it come on twice.
>
> Remember that both www.autozone.com and the UK site
> http://www.honda.co.uk/owner/workshopmanuals2.html
> have detailed guides for your Honda. At the UK site for my 91 Civic (1.5
> liter), I used the Concerto manual a lot. It's engine is the same or
> identical to my Civic's.
>
> I took off and disassembled my Civic's EACV this summer while
> troubleshooting idle problems, but could have spared myself this trouble
> had I first simply purged the cooling system of air.
>
>

Thanks for the advice Caroline. It seems kind of strange to me that it
took your car 40 min. for the fan to come on. I think mine comes on once
the car is nice and warm and it is sitting idling.

What do you think of the other poster's response about my 02 sensor? Is
it reasonable for it to fail after 14 years and 136k miles? AFAIK it is
the original and I have heard different sides about replacing 02
sensors. I've heard that it is the sort of thing that is either working
or it isnt, and I've also heard it can slowly degrade in sensing
quality. I could see a bad 02 sensor causing my problems, but I have
also have heard the many stories about air in the cooling system causing
similair problems. I guess I hope there's not something wrong with my
car (running too rich?) that caused the sensor to go bad if it is indeed
bad.

Could my loss in mileage be caused by having some air in my cooling
system? I may be really lucky, but I have had to drain and refill my
radiator a couple times with my current car and a couple with my old '91
Civic DX sedan, and I haven't really had idling/mileage problems
previously. I did my timing belt (and water pump) earlier this summer
and haven't had idle issues until now.

I did forget to mention that my idle is a little off with regards to my
power brakes. Stepping on the pedal causes my idle to dip maybe 100 RPM
, and then it adusts up to maybe 50-75 RPM below my normal (no lights no
brakes, etc.) idle. Maybe this is normal, but I don't remember it on my
old Civic. I have been figuring it is something with the booster, but
maybe it is related to my recent idle fluctuation problem. I have done
the check for vaccum at the check valve on the booster vaccum line and
it was okay.

It looks like I can get a Bosch OE style sensor for around $30 on the
net. If I can get one cheap locally I might just buy one. I just fear
the bolts on the manifold heat shield. I've never tried to unfasten them.

Mark