bighoss77

okay, bought the car like this. 1998 Honda Civic Ex automatic. Runs fine when first started, idle is a little high. Then, when the car warms up it starts to surge up and down, up and down... sometimes it will just idle really high at like 2200rpm... It had a code for Idle Air Control Valve circiut... So, what I have done this far: I have replaced the IACV with a brand new one from the parts store = no change. Tested TPS sensor = has .5v at closed and 4.7v at wide open. I have sprayed around the TB gasket and IM gasket with ether/starting fluid and got no change. My temp gauge and cooling fan works, so I'm assuming my temp sensor is good. I can put my hand over the TB and it feels like its going to suck me in and the car will die, so no vacuum leaks. I can put my hand over the passage/opening for the IACV and it will just about suck my finger in, but the car will idle just fine then! also, not sure if it is normal or not, but with the KOEO I can hear the IACV humming/buzzing... If I unplug it and plug the old one back in it makes no noise... so maybe the old one WAS bad, because it makes no noise and the new one is making noise so its good??? I dunno whether its supposed to or not. Its really driving me nuts, I dont know what to check or do next...

ezone

You can't tell this without a scanner. It's completely separate from the gauge and fan units.
Sounds right.
That stuff is explosive! I'd use carb and throttle cleaner, it's only flammable (not quite as dangerous).
Vacuum leak somewhere, maybe internal.

In the throttle body, you have one port, or two? Block off both of them?

PCV valve bad?

Did someone crank open the throttle blade stop? (they would have to tamper with the TPS adjustment to make it look right again though)
Is the cable too tight?

bighoss77

you sure its a vacuum leak? I can put my hand over the throttle body and the car will die out, which makes me think its good and sealed... this car just has the one opening inside the TB on the bottom, and then another at the top for the MAP sensor. Throttle blade is all the way closed when it should be, cable is not too tight. And I dont think I have a pcv valve... its just a hose with a clamp that goes into the valve cover... Also, should the IACV make a humming noise with the key on engine off? the old original one doesnt, but I dunno if that one is good or bad... I drove it to the parts store, Im getting a code for oxygen sensor lean and again code for the IACV

ezone

No, I'm not sure.....But when you blocked the port in the throttle body---the air that allows the engine to continue running has to be coming from somewhere. (A PCV or a stuck IAC is usually considered an internal leak.)

How much did the RPM fall when you blocked off that port?

Does this engine use the IAC mounted on the bottom of the throttle body?


If it is not an external vacuum leak then it could be leaking from the throttle plate slightly ajar? (This is why I said someone would have to tamper with the TPS to get this voltage to look right)


Couple thoughts:
When fully warmed up, the only time it should surge repeatedly is with TPS voltage reading closed throttle plus excess RPM (decel fuel shutoff in action). Something must be allowing too much air to enter the engine somewhere.

If the Coolant temp sensor is not accurate (reads very low temp), it could allow the high idle speed without surging even though the TPS says throttle is completely closed.


Does that help any?

bighoss77

temp gauge only gets about quarter way up when "warmed up"... one thing I did just now... I unplugged the PCV hose and capped it off at the minifold. No change. I put my finger over the IACV port to block it... it was sucking like crazy and the idle went down to normal... around 750-800rpm or so it sounded... but heres another thing interesting... I unplugged the IACV while the car was running and put my finger over the port and it was still sucking like crazy and when I did the rpms went back down to about normal sounding... should the port be close or something if the IACV is unplugged? or should it be mostly closed with it plugged in while running?? I also tried again with a piece of flat rubber to block the whole throttle body opening while the car was running... it alsmost sucked that piece of rubber and my hand in there! lol and the car died out immediately, so I BELIEVE there is NO vacuum leak from the throttle blade back to the head...


oh, and yes it uses the IAC under the throttle body with the 2 ports for coolant facing direcly downward, not the one with the bendy looking ports coming out of the side

ezone

It might not be getting warm enough.
180*F and up is normal operating temp. Check with a scanner that can read live engine data.


There's 20" of vacuum no matter where you stick your hand. It's gonna feel like it's sucking you in.
What did the engine speed do at this point?

======================

When the IAC valve is disconnected, the engine speed is supposed to

increase -- A/T and D16Y7 engine
decrease -- D16Y5, D16Y8 with M/T B16A2

(According to the info I have)

bighoss77

unplugging the IAC while running changed it from a slow rev up and down kind of idle to a real fast paced rev up and down idle... basically it just sped up the idle jumping in repetition. Also, I thought I was plugging the port for the IAC completely making the car run normal... but in fact if I completely block it off (keeping the throttle bore open) the car will in fact shut off also.

I dont have a scanner, especially not one that can read live data like the op. temp., I know the car is getting very warm because the coolant is definately flowing (judging with radiator cap off) and steaming some (not running hot or boiling)

so Im hearing another buzzing noise with key on engine off that I cannot explain... aside from the IACV buzzing when plugged in and key on engine off. Strang thing is, with my stethoscope its most audiable coming from the transmission if putting the probe end directly on the transmission case.... the farther away from the trans I get, the auidble the noise is using the stethoscope... Have no idea if this is related or not. I did try unplugging EVERYTHING on that side to see if it would go away to no avail... I unplugged the little trans solenoids, the speed sensor, the other sensor on the back of the trans, the dizzy, both temp sensor, vtec solenoid, oxy sensor, map, tps, whatever that is on the fuel rail, ect... nothing made the other buzzing sound go away....

okay and also, could it be my ECT sensor is bad? I would replace it, but there are 3 of them that are identical. One under dizzy, one just to the backside of the dizzy and one in the water neck to the rear of the engine... which is which?

bighoss77

so basically the only thing(s) that are going to make this car have a bouncy idle are going to be, IACV, TPS, MAP, ECT, possible air pockets or vcuum leak...? I tested the TPS and it read good, the IACV is new, when I unplug the map sensor the idle drops and goes somewhat steady, but its kind of a rougher idle which most of the time means its working okay, when I unplug the ECT the idle changes from slow bounce to higher bounce, so I think its working.... The car shuts off when you cover the TB, so no vac leaks...? Im stumped.

ezone

So it sped up the idle RPM when you unplugged it and you have an automatic trans, should be normal.
Apparently the IAC is supposed to be good. (apparently)
Now it sounds like the IAC alone is responsible for the high engine RPM.
That doesn't necessarily mean the IAC is bad, just that it is now identified as the source of the high RPM problem.

If the top radiator hose is 180* or higher, most people won't be able to hang on to it for more than a couple seconds.
Some would be able to hold on to it at well over 210 degrees.
Others would scream at 150*.

*I* used to be able to pluck ears of corn out of boiling water. How long do you think I could hang on to it?

This, and what you wrote....neither are accurate tests.
Plus, I still want to know what the computer is seeing as far as a coolant temp input.

Is it still setting this code now?
What other codes does it have? (there should be many if you unplugged everything from the transmission)
If you clear out the codes, what codes come back?

I can't tell you if this is normal or not. I don't recall ever noticing it, but I wouldn't be at all surprised if some do.

It's all quiet over here. (Actually, there is a 2 y.o. here now, I can't hear anything else LOL.)

No clue here.
Possible, that's why I want to know about engine operating data.

None are even remotely identical. All 3 are very different.

Sensor with 2 wires is for the computer.
Sensor with a single wire is for the temp gauge.
Google:


Radiator fan switch.

bighoss77

I dont have a single wire temperuture sending unit... all 3 on this car have 2 wires and share the same exact round style plug. But when I unplug the one for the computer reference, it does the same exact thing as if I unplug the TPS, IACV, when the car is running... the idle jumping just occurs more rapidly and will continue to do so even after I plug whichever one back in that I unplugged. Then shut the car off, crank it back up and it will go back to the "normal" idle hunt - kind of a slower repetition of up and down idling. IF I unplug the MAP sensor, the idle will smooth out and be about 900 rpm, but not a "smooth" idle if that makes sense... sounds like a "rich" type of idle. Again even after its plugged back in it will run like this untill I shut the car off and crank it back up... In gear the car idles normally and can be driven, except when cruising and you let off the gas the car will jerk hard, then get back on the gas it will jerk hard again... after googling this problem it seems to be a comming issue with the jerking and the idle problems... Most say it was due to a vacuum leak, but I have literally soaked the TB and intake manifold and all hoses and vac lines last night and it did not change anything with the idle. I also covered the TB again with a piece of thick rubber and it shut the engine off like it should. Im to the point where Im just going to bite the bullet and take it to and old electrical automotive guru that only few know about around here and just pay him to diagnose and fix it... just sucks because the car was bought for $400, already have $350 in other repairs on the car, was planning to have $1000 or less in the car and sell it for $1500-$2000. Theres goes the profit!

ezone

You sure? My wiring diagram shows a single wire temp sensor for the gauge for 96-00, with the same pic I lnked earlier.

No biggie, NVM.

There's a reason it was dirt cheap.


I think you need to figure out why the IAC is being held open too far, since it appears this is the source of your issues....
(Have you tried tapping on it yet? Maybe it is stuck open.)

Got a way to read some basic engine data yet? A cheapcheap code reader won't, but the next step up from that might.

Got anyone close by with an identical car that works right? Swap the computer out of it and see what happens.


Gotta run for now...

bighoss77

yeah the reason it was cheap is because the harmonic balancer came off! lol. The keyway broke. It only managed to chip the very front of the crank, so it took a new key just fine and the new balancer went on great. They thought it was going to need a crank/motor... I fixed it and the rest of the car is kinda beat up, so $400 wasnt a bad deal IMO. I mean once you get going down the road or have it in gear it seems to run good. I just can't figure out the idle problem and other symptoms associated with it... I just dropped it off at guys place to get looked at... I'll report back with what he says about it next week.