Accord: Idle to high and irregular, no error code
JD
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When started cold, the engine goes to 2000 RPM and drops after 2 second to
1800 RPM (should be 1400 +/- 200 according to Haynes manual). The RPM are
read from the tachometer in the vehicle. When warming up (just over the
blue) it goes gradually down to 975 (should be 770 +/- 50). If I open and
close the throttle it goes up to 1200 and back to 975 after 2 seconds.
When getting warm (about 3/8 on the temp meter) the idle goes up to 1200.
Here's also where the irregular idle starts. After driving and waiting
before a red light, The engine hunts between 1200 and 1500 RPM. It goes up
to 1500 RPM in about 1 second and the drops quickly back to 1200 RPM. After
a drive on the high way it's the worst. The temparature indicator is just
below the middle when the engine is warm. If I unplug the EACV the car idles
at 975 with the idle control screw already at the minimum (I also found out
somebody had turned the idle adjustment screw with force so I had to take it
out and replace it)
The biggest problem: The computer gives no error code. The engine sounds
good and runs fine (except for the bad idle) Opening the throttle slightly
removes the hunting. If I turn on a high electrical load (eg Airco, Blower
and lights) then most of the time the hunting stops and the car idles at
1200.
Checked
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To try to solve this problem I cleaned the Idle Air Control (IAC, sometimes
called EACV) valve and the fast idle thermo valve with carburator cleaner.
Also sprayed a bunch of cleaner in the throttle body. Cleaned the cooling
lines to and from these valves. Checked the engine timing and valve
clearances. Replaced the cooling water engine temperature sensor. Removed to
connector from the alternator and run the car on the battery. Check the
voltage from the battery and altenator. Could not find a vacuum leak either.
Nothing helped so I went to the local dealer. They replaced the complete
throttle body and both IAC and fast idle thermo valves. They checked that
all the vacuum hoses where correctly connected. Nothing helped. Then they
quit and said they could not find it.
What next
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Could this be the distributor or a crackshaft position sensor?
A EGR valve which stays open? (I tried disconnecting the vacuum hose to the
valve, did not help)
Computer error? (Computer gives error code when I remove a connector)
Leaking inlet manifold?
Heeeeelllllpppp,
Jan Derk
JD
The engine has 160,000 KM. And to be really honest the car is a Rover 620i,
but under the hood it is exactly similar to a Honda Accord and there does
not seem to be a Rover news group.
Jan Derk
Arthur Russell
If you disconnect the electrical connection from the EACV does it affect
the idle (either the fast idle, or the hunting) does it produce an error
code? (it should) With the connector unplugged, this valve should slam
shut. If your problem completely goes away, then it may be that your ECU
is being lied to by a sensor or a wiring problem, or the ECU itself has
failed.
Is your engine actually getting up to the correct operating temperature?
If not, the thermowax plunger in the IACV may be only partially closing
its valve. This can cause the hunting behavior you mentioned.
Can you affect the symptoms by turning the steering wheel? Idle on some
(all?) Accords also depends on P/S pump load.
-Arthur
JD
> If you disconnect the electrical connection from the EACV does it affect
> the idle (either the fast idle, or the hunting)
The RPM drops back to 975 RPM and the hunting stops. But the RPM is still to
high with the adjustment screw on the minimum. So I think that there must be
some other problem causing the to high idle and the ECU responding to it. My
question: what else can cause a to high idle. Can idle also be to high if
the engine gets too much fuel? Maybe the ECU responds to that.
> does it produce an error code? (it should)
Yes it does. I always have to reset the computer by pulling the Backup fuse
for 10 secs.
> With the connector unplugged, this valve should slam shut.
The valve closes well. I disconnected the EACV (with the cool water still
connected) and closed the 2 holes with a piece of rubber. This has exactly
the same effect as removing the electrical connection.
> If your problem completely goes away, then it may be that your ECU
> is being lied to by a sensor or a wiring problem, or the ECU itself has
> failed.
When disconnecting the EACV the hunting goes away, but the high idle does
not. I thought of the ECU myself as possible culprit, but I do not have
another one to check it out (I'll ask the Rover/Honda dealer if I do not
find the problem soon).
> Is your engine actually getting up to the correct operating temperature?
> If not, the thermowax plunger in the IACV may be only partially closing
> its valve. This can cause the hunting behavior you mentioned.
The temperature gets up to just under the middle of the gauge.
> Can you affect the symptoms by turning the steering wheel? Idle on some
> (all?) Accords also depends on P/S pump load.
No, turning the steering wheel or braking does not signigicantly influence
the high idle or hunting behavior.
JD
Arthur Russell
unplugged? When mine is up to temp, pulling the EACV connector causes
the idle to go to about 700 (spec is 700 +/-50 if I recall) Yours is too
fast, and I would guess you have an additional source of air past the
throttle body. I have a couple thoughts:
1) Do the same test as you did for bypassing the EACV (plug with rubber
flap etc.) for the temp controlled fast idle valve (the non electrical
one) to rule that out. You said yours is new, so that's probably not it.
2) You mentioned that the idle screw itself had been buggered, and that
you replaced it. Depending on how it was previously abused, the seat
that the screw needle mates with may have been damaged. If so, that
could cause excess air past even with the screw all the way in. I don't
know if you can replace the seat separately, but that would be nice.
3) Air leak after the throttle body? Use a plant water sprayer and
sequentially soak things to see if you can stop/isolate an air leak.
Check hoses etc. really carefully.
4) OK, so no vacuum leak, both valves fully closed, and idle set screw
is OK? One question here would be where is the air coming from which is
allowing the engine to run? (check remaining sources like PCV valve, EGR
valve, brake booster (Aha, this is a good one to check) Just pinch off
various vacuum lines) I'd start with the brake booster. I can cause my
idle to increase noticeably if I pump the brakes rapidly.
5) How's the throttle body really work? Does it completely close up, or
does it leave a slight gap? Could it be leaving too much of a gap?
Again, yours is new now, so that probably isn't it. However, is the
accelerator pedal free play OK? Is the cruise actuator (if you have one)
possibly binding up?
6) What are your emissions like at idle? Can you check the voltage out
of your O2 sensor when the engine is warmed up, at idle?
-Arthur
JD
> unplugged? When mine is up to temp, pulling the EACV connector causes
> the idle to go to about 700 (spec is 700 +/-50 if I recall) Yours is too
> fast, and I would guess you have an additional source of air past the
> throttle body. I have a couple thoughts:
haynes manual
Engine idle speed: 770 +/- 50 RPM
With EACV disconnected: 620 +/- 50 RPM
> 1) Do the same test as you did for bypassing the EACV (plug with rubber
> flap etc.) for the temp controlled fast idle valve (the non electrical
> one) to rule that out. You said yours is new, so that's probably not it.
I did: No effect. Hunting and high idle remained. My fast idle is not new,
but the Rover dealer temporary replaced it with one from a working car.
> 2) You mentioned that the idle screw itself had been buggered, and that
> you replaced it. Depending on how it was previously abused, the seat
> that the screw needle mates with may have been damaged. If so, that
> could cause excess air past even with the screw all the way in. I don't
> know if you can replace the seat separately, but that would be nice.
The throttle body was exchanged completely with one from a working Rover
620i by the Rover dealer. No difference. So we can exclude the throttle
body.
> 3) Air leak after the throttle body? Use a plant water sprayer and
> sequentially soak things to see if you can stop/isolate an air leak.
> Check hoses etc. really carefully.
I'll do.
> 4) OK, so no vacuum leak, both valves fully closed, and idle set screw
> is OK? One question here would be where is the air coming from which is
> allowing the engine to run? (check remaining sources like PCV valve, EGR
> valve, brake booster (Aha, this is a good one to check) Just pinch off
> various vacuum lines) I'd start with the brake booster. I can cause my
> idle to increase noticeably if I pump the brakes rapidly.
I pinched off all vacuum lines. Engine vent, brake, all small vaccuum lines.
No influence.
> 5) How's the throttle body really work? Does it completely close up, or
> does it leave a slight gap? Could it be leaving too much of a gap?
> Again, yours is new now, so that probably isn't it. However, is the
> accelerator pedal free play OK? Is the cruise actuator (if you have one)
> possibly binding up?
I do not have cruise control and the free play is set correctly. It does not
open the throttle valve. A not so smart mechanic even adjusted the small
screw (which you're not supposed to touch and after he exchanged the
throttle body with a known good one) which sets the minimum position of the
throttle valve. Causing the throttle valve to stick in the minimum position.
I changed this screw untill the position that the throttle just did not
stick anymore.
> 6) What are your emissions like at idle? Can you check the voltage out
> of your O2 sensor when the engine is warmed up, at idle?
I was said that the all emissions (O2, CO2, HC and lambda) were good when
the idle is steady at 1200 RPM. The car does not always hunt. The hunting
starts when the engine is warmed up well (eg after a piece of highway).
When it starts hunting the O2 is to high, the Co2 to low and the HC to high.
Looks like overly rich.
JD (who is going out with his plant water sprayer to diagnose his car :-)
Arthur Russell
have my service manual with me at work! I don't want to spew false
recollections etc.
In your last post, you mentioned that it appears to be running rich when
the hunting occurs. Could it be that the MAP sensor is faulty? Then the
ECO would think more air was getting past the throttle, and would
increase fuel accordingly. Would this cause hunting behavior? I'm all
out of ideas.
Good luck, there are other folks here with much more expertise about
this kind of stuff. Maybe they can shed more light on your problem.
-Arthur
JD
If you're interested. I've also opened another thread on this subject in the
rec.autos.tech newsgroup with some interesting replies. Thank for your help.
I try to locate the problem using your hints tomorrow as it is dark and
raining now here in Amsterdam, The Netherlands.
JD
JD
the throttle body inlet with a piece of rubber. The engine kept on running.
So it had to get air from somewhere. I checked the idle screw and all other
tubes again. After that I di some more spraying with contact spray and there
it was. Spraying on a hard to reach spot (why does it always have to be hard
to reach) between the upper and lower part of of the throttle body stalled
the engine. At a closer examination I could see piece of gasket sticking out
where it should not be.
I'm off for new gasket. Thanks for all your help.
Jan Derk