Is my Idle Air Control Valve bad without a CEL?

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This topic contains 18 replies, has 7 voices, and was last updated by EricTheCarGuy 1 EricTheCarGuy 9 years ago.

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  • #448210

    Eric, great write up in the Honda idle issues thread. I posted there but didnt get a response so decided it was probably best to copy paste here:

    I have some suspect issues with my vehicle and wanted to contribute to your ongoing ‘Honda idle’ thread. Here’s the scoop…

    Vehicle: 1992 Honda Civic VX (Canadian Built, Canadian VIN, if that matters…no fit valve on this engine; 1.5L D15Z1) …I live in the south-eastern US.

    The engine seems to be experiencing an occasional sticking of the IACV(as far as I can tell). For instance, when coming to a stop light, the engine RPMs will have the ‘raise/fall’ symptom happen, at times, occasionally. It was cleaned before, to fix the raise/fall, but symptoms seem to start back more so in colder weather; but progressively I’ve noticed another symptom.

    My question is, would a sticking IACV ‘also’ cause issues like a rough or low idle/RPM lug? This happens at full temp only, as the cold start seems to be just fine around 1,500 RPMs or so.

    Here’s a scenario, when waiting in line at a drive thru, traffic light; etc, night or day. The engine will start to ‘lug’ and cause some chatter/vibration (feels like the engine wants to shake or shimmy at times it gets so low? heh), the ‘lower’ tach mark is where the RPMs are when this is happening. I’ve heard that represents 500 RPM and others claim that is the stall mark(is it true the stall mark and 500 reading are very close together?). That sure helps when saying what it’s idling at, so I need clarification there. To me it appears to be just under 500 RPM when this is happening, sometimes appearing lower than that(if I read the tach correctly). When this happens, if I turn the A/C on, apply the brakes, those sort of things(cooling fan comes on will sometimes trigger the event), then usually the idle raises about 200-300 RPM or so, and feels much better no lug/vibration issues of obvious nature; when it’s then around 750-800 RPM.

    My idle ‘looks’ similar to this ‘newer’ VX(an HX model) Civic video on YouTube, and has similar symptoms as the description laid out, my tach would read lower than his, but my temp is higher on this gen’s current display.:

    Here is the original PCV valve:

    If this can cause an idle issue I may change it to check it off the ‘list’ anyway. The PCV valve on this car originally was located down at the ‘breather chamber’ underneath the runners nearest the distributor, seated into the chamber itself. So, my ‘elbow’ location at the Intake Manifold has the ‘hollow elbow’ instead of the PCV valve, makes replacing a pain if OE dealer was ‘upgraded’ to go into the runners on the manifold itself(sigh). Not sure what the dealer has, but wanted to clarify which PCV valve is in use currently.

    Spark plugs replaced last summer(I over dosed slightly on some Red Line SI-1 FSC, suspected reason for the red blotch):

    I’ve had the following jobs/work done on this vehicle(260k miles currently; owned since 230k):

    Clutch w/ an EXEDY ‘OE’ + Flywheel re-surfaced w/ rear main seal replaced (December 2011)

    All brakes(save for the rear wheel cylinders/hoses)…brake fluid ‘normal’ flush by repeated bleeding, same for clutch’s ‘brake’ fluid

    Timing belt + water pump and their relative seals; along with drive belts…at about 240k

    Radiator cap(Honda), the heat works great and it rests slightly under the ‘mid’ point on the temp gauge.

    CVs twice(one reman failed after only 1 year…lame, got some ‘new’ GPS brand CVs from AAP with lifetime warranty we’ll see…if problems I’ll go dealer $$$)
    replaced axle seals as well

    Inner & Outer tie-rods + bellows(last summer)

    Valve adjustment(by a honda tech, 1 year ago) + VCG

    EGR valve + port cleaning(2 years ago)

    IACV valve cleaning(2 years ago, gaskets were left alone?)

    replaced leaky vtec solenoid + housing gaskets(1 year ago)

    Distributor cap + rotor, OE NGK 4043 plugs( ZFR4F-11) + Sumitomo wires(OE brand new) 2 years ago

    CEL, code 48: Replaced ‘original’ 5-wire LAF(02) sensor with an SG335(SMP brand), works great no CEL currently, not for over a year now)

    Change the oil with a full synthetic every 5,000-7,00 miles with Used Oil Analysis to back it up(I post on BITOG site)
    Changed the transmission fluid several times now, I’ve used PEA based fuel system cleaners, replaced the fuel filter twice(for kicks, before I knew better, a little more OCD).

    Not sure if this is making the ‘feel’ worse, but I ‘do’ suspect the motor mounts need replacing(some at least?).

    When I’m driving in gear, holding steady for instance in any gear, and I let off of the throttle I get an either ‘delayed’ or ‘immediate’ rocking sensation. Like the engine is trying to rest but I can feel it doing this, not extreme necessarily, so IDK. Having my clutch’s master cylinder replaced this week so I’ll ask the shop to look at the mounts. Also, while this ‘same’ shop did the clutch job, they also had the car stall on them during test drives. I’ve also had the vehicle stall easily twice in the 2+ years(30k miles owned) trying to move from a stop while going uphill. ???

    Those are perhaps anecdotal, but may point to a sticking IACV or even perhaps engine mounts(EDIT: I noticed in your suspension vid maybe strut bar or control arm bushing instead of mounts)? That’s my suspicion as of now. If this can confirm the IACV sticks anyway. I’m thinking of removing it myself with the engine cold, replacing the screen and using some tb/intake cleaner on it. If the hot idle ‘also’ improves doesn’t this mean the IACV was/is the issue? If it returns promptly, would a new IACV be advised? Thank you.

    Any more info feel free to ask.

    The engine was compression tested 2 years ago, it passed. Coolant is full at the radiator cap when cold, though the level goes down from the reservoir over time; the water pump seems to weep a bit at the lower timing cover weep hole(no coolant visibly on the ground where parked nor any coolant smell but visible from the weep hole, manual says this is normal?) My UOAs don’t show any coolant either. 1 quart of oil is consumed every 4,000 miles, so the rings are still okay, etc.

    Thanks again for your work and the info already out. I’m a mechanic in training.


    Today, the idle lugged really bad at idle. It almost wanted to stall and was really low. No oil pressure light and the engine runs great otherwise. I didn’t have time to remove the IACV, so I sprayed TB cleaner at the port for the IACV external side of the butterfly while blipping the throttle to keep the car from stalling. It stalled 2 times anyway, heh.

    I didn’t think to plug the hole and see what happened to the idle at the time. Is that a good method to diagnose IACV function? If the idle lugs again really low as described previously, and I plug the port with my finger(with a glove as this is a full temp ‘check’) and the idle stabilizes/stops lugging, does that mean the IACV is plugged/bad?

Viewing 3 replies - 16 through 18 (of 18 total)
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  • #448226

    ^Ah, don’t know why I didn’t remember that, it was literally about 15 seconds of run time then shut off to move the car that morning before the restart later(was half asleep so wasnt thinking lol). I’ve had the ‘flooded cylinder’ issue before when doing intake cleaning. I also had to use the clear flood pedal to the floor to get it to run.

    Makes complete sense and it isn’t a recurring thing so chalking it up to fuel choking the mixture is right on. Also, good to note about the sensors in question. I had the infamous 02 for these lean-burn which have the really expensive 5-wire 02/LAF sensors when I bought this car. No idea how long it had been allowed to run in open loop by the previous owner, and for a lean-burn engine doubt thats a good thing. Especially for the cat, so far emissions are passing though. yay, had some high HC numbers when I bought the car, but got it fixed eventually.

    I actually prefer top-end foam cleaners, at least on non-MAF equipped intakes; and as long as actual sludge isn’t present(engine in ‘relatively’ decent shape), but only had some TB/Carb cleaner to hit the IACV the other day with.


    Here’s an UPDATE: I still believe it’s the IACV just making a note of a current symptom:

    Today, while the engine is at full temp and upon returning home, the idle is basically pegging the stall mark on the RPM tach. ?!

    This is again an instance of the lug present which led to this thread. I’ve since bled the cooling system but will need to do this again since my overflow tank is dry. I have performed UOA with no sign of coolant in the oil and I don’t get a drip on the ground; though an occasional slow weep(just a drip hanging from the lower timing belt cover(which has been warped from years of heat I’d imagine? and it isn’t flush against the oil pan any more like it was stock. FWIW, IDK?

    So, I’m in Neutral ready to shut the car off, it’s idling really low. I perform two rev’s to 6,000 RPM(near redline) and each time as the RPMs come back down, once they enter the area relative to engine controlled idle(as it drops down below 1800 RPMs visually, not sure but this tach is somewhat delayed).

    Anyway, as it enters this range while falling, there is a ‘wobble’ or ‘shaky’ feel to the engine idle as the engine idle control mechanisms takes over before it decides to just ‘bottom out’ again near stall mark. When I punch it a 2nd time after letting the idle do whatever it was going to do for about 10 seconds, it does the same thing. There doesn’t feel like there is any hesitation and the engine ‘feels’ here.

    I purchased a battery load tester like Eric has in one of his videos on voltage drop testing, IIRC?, but anyway I think my battery may only be marginal so I’m not sure if I’ve got multiple contributions to the symptoms.

    EricTheCarGuy 1

    The coolant leak from the timing cover is probably the water pump, I would recommend addressing this leak as it won’t likely get better on it’s own. As long as you bled the cooling system according to the video you should be able to rule that out. I don’t know if this has been mentioned but if someone has messed with the idle screw it’s possible it’s out of adjustment and the computer is trying to compensate for this by adjusting the idle it’s just not able to do it successfully because the base idle is incorrect. Also I don’t remember if you checked for vacuum leaks or not but this is also a basic step that needs to be performed if you have an idle issue. In addition you need to make sure you have an OE PCV valve installed and that there are no leaks in the system.

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