Erratic Idle

Took my 98 dx 5spd to the shop today and asked them to check my IAC.
Which I will check myself. There is some crappy air intake on the car
and the people at the shop said thats what was causing my up and down
idle. Can a crappy air intake cause the same issue as a malfunctioning
IACV?

 

Took my 98 dx 5spd to the shop today and asked them to check my IAC.
Which I will check myself. There is some crappy air intake on the car
and the people at the shop said thats what was causing my up and down
idle. Can a crappy air intake cause the same issue as a malfunctioning
IACV?

An engine needs air in order to runs. If it does not get the air that it
needs,it could effect the way the engine runs. You should remove the
crappy air intake and visit a auto shop or junk yard place a air intake
system on the car that has a new filter. After you do that--take it back
to the shop and have them recheck the IAC. You may want to ask your
friends if there are any stores that sell after market air intake systems.
visit this site:
andysautosport.com

 

The "crappy intake" can foul the IAC with carbon and grit, so it's unable
to adjust the idle properly and you get a great big air leak.

A quick test:
Warm the engine up to full hot and keep it running.
Pull the "crappy intake" so you can see into the throttle body.
There ought to be a port visible in the throttle body.
Partially cover the port with your finger. Does the idle settle down?
Keep covering more of the port until the idle settles down.

Does it eventually settle down? If so, the IAC isn't moving correctly.

Do you see TWO ports in the throttle body, or just one? If your car has TWO
ports, then the lower one leads to a Fast Idle Valve. This should NOT be
admitting air when the engine is hot. If it does, the Fast Idle Valve is
bad, usually the result of a sludged cooling system.

Also check for other sources of air leakage, such as a vacuum line
disconnected.

 

Erratic Idle? Isn't that Eric Idle's twin brother?

 

have you checked the coolant level in the radiator? if it's not full to
the top, it can cause idle problems because one of the sensors is not
fully immersed.

 

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Beyond that, the reservior needs to be full too, since trapped air can't
escape if there's no coolant in the reservoir to replace it.
Honda premix is the foolproof thing to try first. You might have to top
it up to MAX twice.

'Curly'

 

A quick test:

it never settles out

 

OK! I found out something today. The erratic Idle stops when the AC is
turned on! The AC has to be turned on though, It can't just be the
blower/fan. The AC also makes a whistling sound. Any idea why it
idles normally when the AC is turned on?

 

Engaging the A/C kicks up the throttle a bit to compensate for the
additional drag of the compressor.

I'd really be suspecting a vacuum leak at this point.

 

Anyone know what the best way is to find out where the vacuum leak is?

 

A good pair of humanoid auditory sensors.

 

Since most vacuum leaks come from cracks in the rubber vacuum hose where it
attaches to nipples in various places (okay, guys, wipe those weird images
out of your minds!) you can take any of the common approaches:
*buy a bunch of vacuum hose in all the sizes you see under the hood and
spend an hour or so replacing them all. The cost is reasonable and the
benefits are lasting.
*feel near the end of each hose for cracks and replace or trim the cracked
end from the bad one(s). Repeat next time there is a vacuum leak.
*if you can hear a whistle, try to isolate it. It isn't easy, but combined
with the change in pitch if you get your finger on a crack it may pan out.
Repeat next time....
*buy a vacuum pump/guage combo - about $30 US IIRC - and see which hoses
that come off the intake manifold hold vacuum. It is also possible to do it
with the suck to draw a vacuum and place your tongue over the end to see if
it holds, but that is really the po' boy's method and can get you an odd
reputation. Repeat next time....

Mike

 

I had a leaky vacuum-advance diaphragm on my Accord's distributor that I
didn't know about because it wasn't audible like a leaky hose tends to
be.... I found it by pinching off the vacuum hoses (gently, with
non-serrated pliers) one at a time until pinching one caused a
noticeable change to the engine sound, speeding up a bit and smoothing
out. Start where the hoses come off the carb, throttle body, and/or
intake manifold with this one, and if you find one that has an effect,
you can move outward from there.

 

I had a leaky vacuum-advance diaphragm on my Accord's distributor that I
didn't know about because it wasn't audible like a leaky hose tends to
be.... I found it by pinching off the vacuum hoses (gently, with
non-serrated pliers) one at a time until pinching one caused a
noticeable change to the engine sound, speeding up a bit and smoothing
out. Start where the hoses come off the carb, throttle body, and/or
intake manifold with this one, and if you find one that has an effect,
you can move outward from there.


That's a unique method. It's far superior to the method that I learned. We
learned to remove each vacuum line and pinching off one end while we
blowed into
it as hard as we could. They now have a device called a "vacuum/pressure
tester" that makes it easier. However, you method would work in some
cases.
Jason

 

I'm going to try this method. What size hoses do I need for a 94 Civic VX?

 

We could give you a lot of inaccurate answers and maybe an accurate one ;-)

Just do a quick survey under the hood, even take snips of the ends of each
different sizes you see (should only be two or three sizes) and estimate the
total length of each size. The hose is sold by the foot, so you'll want to
do the "Price is Right" thing: buy at least enough, but try to go over by as
little as you feel confident about.

Mike