1990 Honda Accord Idle fluctuation

My 1990 Honda Accord 2.2L started to have idle fluctuations
yesterday. The RPM will fluctuate between 1700 and 1000 RPMs when the
car is stopped. The fluctuations don't seem to be noticeable when the
car is in gear. What would cause this? I searched for vacuum leaks
but couldn't find anything. I recently did a tune-up. Please help!

 

A strong candidate: Top off and monitor the cooling system. It cools certain engine
control sensors. If they are not fully immersed, then the wrong signal gets sent to the
engine control computer.

You should do a proper purge of air from the system as well, though its said over time the
air will vent itself. I prefer going through the roughly half-hour, fairly easy, idle
purge procedure described in the owner's manual and Factory Service manual.

 

The coolant system is working properly. Any other ideas?

 

wrote in @s12g2000prg.googlegroups.com:

I'll bet the fluctuations are only when the car is warm.

If so, it's a stuck Fast Idle Thermo Valve. There is a way to test for
that.

 

replace the PCV valve, and clean the Mass Air Flow (MAF) sensor,
remove the idle screw and clean the assembly with carb cleaner

if that doesnt fix it then check the Idle Air Control Valve and adjust
the Fast Idle Valve,

excerpt: "its the cylinder on the driver side of the intake manifold,
with the triangular cap with 3 screws. pull them out and take the cap
off, and twist the outer white ring clockwise until its as tight as
possible, and close it back up."

http://www.honda-tech.com/zerothread/1704468

 

wrote in @d27g2000prf.googlegroups.com:

This car doesn't have a MAF.

You can't "adjust" the Fast Idle Valve. It gets stuck open on account of
neglected coolant changes and results in a massive air leak when the car is
warm.

The Fast Idle Valve on this car has two screws, has no white ring and is
non-adjustable.

 

| What would cause this?

Mine had this problem, cause was throttle angle sensor
( a variable resistor ). See
www.autozone.com/servlet/UiBroker?UseCase=RG001&UserAction=processModel&Parameters=001

 

Yes! the fluctuations are only when the car is warm. How do I test for
a stuck Fast Idle Thermo Valve?

Thank you,
Paul

 

--------------------------

Before getting too far into it, how full is your coolant reservoir? You
said you did some work on it. Did you make sure the cooling system was
full to the MAX mark afterwards? I think it's mentioned in your owner's
manual.

'Curly'

 

The Fast Idle Valve is a round, sort of tower-like thing to the left
(driver's) side of the intake manifold, between the "PGM-FI" logo and the
valve cover. It has two screws on top of it that hold a sheet-metal cover
in place.

With the engine fully warmed up and the idle fluctuating, remove the two
screws and the cover of the Fast Idle Valve. Feel the valve seat area with
your finger. If there *is* air flow (suction), the valve is stuck open. You
will probably find that once you cover the valve seat with your finger the
idle will settle down.

 

I finally got around to trying to fix this again. I removed the 2
screws and sheet metal cover to check the Fast Idle Valve. I didn't
feel any suction or airflow and couldn't get the idle to settle down
by covering the valve seat. Thanks for your help Tegger, but I guess
the Fast Idle Valve is not the culprit. Does anyone else have any
other suggestions??

Mostco, the coolant is full.

TE Chea, your link no longer works. Is there a way to test if the
throttle angle sensor is bad?

Thanks,
Paul

 

-------------------

The rad has to be full as well as the reservoir. How full is the
reservoir, just a puddle in the bottom ? ? (that's called empty)

On a 1990 I think the system has to be 'burped' (manually), but it won't
work if there's no coolant in the reservoir to displace the air.

'Curly'

 

Both the reservoir and Radiator are full. I will try burping it, but
I really doubt that is the problem. It was working fine for awhile
before this problem started.

 

Another air-related suggestion: When the car is warm and the idle is
fluctuating, remove the air cleaner pipe to the throttle body. Can you
progressively cover the throttle body with your hand to the point where the
idle settles down?

What happens if you unplug the EACV? That's the idle air control valve
behind the throttle body. Sometimes a stuck-open EACV causes fluctuating
idle.

And did you check the coolant in the rad, not the reservoir?

 

Yes, if I can cover the throttle body enough to set the idle down.

I unplugged the EACV and the idle jumped up to a fast idle and the
check engine light came on. I had to restart the car before the idle
would settle down again (actually fluctuate again).

Does this tell you anything? Is the EACV the culprit?

Yes, I check the coolant levels and "burped" it also. I am very
confident that there isn't any air in the coolant system.

 

Bingo. You have a major air leak somewhere.

It is normal and expected that the CEL would illuminate when the EACV is
unplugged.

So the idle fluctuates even though the EACV is unplugged?

Hmmm.

You have large amounts of unwanted air entering the system.

Before anything else is done, you need to check each and every one of your
many vacuum hoses, including the ones inside the EGR control box on the
firewall.

You also have an Air Boost Valve. It is at the opposite end of the intake
plenum from the throttle body. With the engine idle fluctuating, disconnect
the Air Boost Valve's vacuum hose and plug the port in the valve with your
finger. If no settling of the idle, this part is OK.

Chek all the bolts/nuts that hold on the intake manifold and other intake
parts. Loose intake parts will leak vast amounts of air.

If the coolant is right up against the bottom of the rad cap, then the
level is fine.

Your focus now is to find that air leak.

If you are 110% certain you have eliminated the possibility of any air
leaks, then -- and only then -- we try readjusting the idle speed screw.

What are these three digits of your VIN (represented here by x's? JHMCBxxx
(No personal information is in those three digits).

 

Sorry, I didn't write that very clear. When I unplug the EACV that
idle jumps up to about 2000 RPMs and stays there. I was trying to say
that if I plug the EACV back in, the idle wouldn't calm down and
fluctuate again until I restarted the car.

So is it my EACV that is the problem or an air leak somewhere?

My VIN is HGCB714

I really appreciate your help,
-Paul

 

You should find a hole in the sidewall of the throttle body just before the
throttle plate. This will be the EACV air intake port. With the EACV
UNplugged and the idle high, is there suction at the EACV port? With the
EACV unplugged, there should be NO suction.

That doesn't seem like an accurate VIN extract. CB7 is the Accord with the
2.2L SOHC. The next two digits are supposed to describe trim level and
transmission, but my docs say "14" is invalid.