Rep Power: 192

2000 DX 1.6L

I notice that as the temperature decreases..
When the engine is cold, I get fluctuating idle when I start the car.
But once I put it in park all idle symptoms go away.

The colder it gets, the more severe the fluctuating (or bouncing up and down from 750-2000 RPM becomes). Even to the point of stalling, during extreme cold weather (Canada).

I've cleaned AIC, and changed distributor, wires, plugs, and air filter as maintenance. Symptoms remain the same. No CEL.

I got an oil analysis from BlackStone Laboratories and everything was fine, no coolant in oil.

Suggestions?

 
Rep Power: 518

Anything that causes the idle speed to be higher than it should, can make the surge happen.
Vacuum leaks and stuck IAC are probably the most common things I saw, also low coolant level.

Get it surging then open up the air breather and use your fingers to plug off the big hole in the side of the throttle body, see if that brings the idle speed down to a normal level or stalls the engine.


Got codes?

 
Rep Power: 192

No Check Engine Light, and no codes reported on my scanner.

I'll try to block the hole when I get a chance to test during a cold startup and report back.

 
Rep Power: 192

Just to note that ALL symptoms immediately go away when vehicle is put into gear. D or R.

I figured anything to do with AIC would not matter which gear the car is in?

 
Rep Power: 518

Free engine speed has to go up to 2000 RPM before the fuel cut kicks in and starts the surge process.
Putting the trans into gear puts a load on the engine so it brings the RPM down to a manageable level for the computer.

Does it surge immediately after a cold start --or does it have to run a little bit before it starts surging?

 
Rep Power: 192

The motor starts as it normally should when cold, with the revs increasing to about 1500rpm, but after a few seconds, it drops to about 750, then back up, then back down...etc.
Each time the range decreases as the engine warms up until it rests at normal idling speed.

 
Rep Power: 518

Hmmm. Seems odd that it would surge while still very cold.

Try plugging the hole as described, that would at least tell if something other than the IAC is allowing excess air in.

Do you have a scanner that can give live operating data?

 
Rep Power: 192

No sorry, just an OBD2 reader.

I'll try that when I get a chance, it's actually been quite warm here lately for this time of year..lol

 
Rep Power: 0

Hi there, i had the same issue in Civic, so i removed the AIC and the throttle body as well as the FITV and stripped it down, then i used the carb cleaner and sprayed it all over to get rid of the ****. I then put everything back and disconnected the battery for 20 minutes. Now my idle is 100% fine

 
Rep Power: 518

^What he said^
Duh, idle relearn.

 
Rep Power: 192

I cleaned my AIC and TB, and I'm pretty sure that I don't have a FITV.
Also, my issue is strictly dependent on temperature. When it's warm, no symptoms.

I'll try and get a video of what happens when it's cold (when it gets cold)

 
Rep Power: 0

I see, same story, Can you send me some pics of the throttle body and the a pic of the back? you could also have a leak somewhere so a pressure test would be a good idea.

 
Rep Power: 192

Hey guys, thanks for replies!
I managed to get a video, it just starting to get cold here, sorry for delay!

The fluctuating starts at around 20 seconds in.
This is mild, but gets much more severe as it gets colder.

Hope this helps, to help me diagnose!?

 
Rep Power: 518

That sure wasn't what I was expecting to see.

 
Rep Power: 192

I took everything apart and cleaned again.
The IAC hole in the TB does stall my car if I plug it. It sucks in air at idle.

The screw I highlighted in red seemed to be a bit loose, it seems to adjust vacuum? I cleaned it and tightened it up.
I noticed a bit of coolant on the TB plate, and it looks like the IAC gasket was a bit flat. Strangely, I am loosing coolant somewhere as I need to keep topping up my reservoir, so will be sure to replace this.

After all this, I started everything up and it seems to idle just fine. Will monitor.

 
Rep Power: 518

So everything is being controlled (or not) through the ECM and IAC, it's not an external vacuum leak.
That screw is for adjusting the air bypass volume...


The passage for the screw can get clogged with the same goo that gums up the throttle plate and IAC so it would be good to clean it all the way out


Problem is I have never had to make that adjustment manually, I've always had a scanner that does the ECM setup for adjusting.

I could take a guess at how to adjust it without the scanner but I can't tell you if the computer would like it 100%......


Does your IAC use a separate passage from the bypass screw?(Are there two big holes in the throttle body or one?)

Get it all warmed up to operating temp and fan cycles, then force the IAC closed (or block its passage if there are two) then use big screw to adjust RPM to 600-650.
Well, the IAC can dump a little bit of coolant when you remove it so that might be what you saw, and the rubber gasket will get hardened over time so it should be replaced so it does not leak into the intake system, coolant in the intake is bad.

 
Rep Power: 192

I first thought the screw was for idle adjustment, but it appeared no matter what setting it only seems to create more suction. I heard about people tightening the FITV, so wasn't quite sure, I figured tight was better than loose. lol

Here's the TB, majority of suction was from the hole at the front. Especially when adjusting that screw.

 
Rep Power: 192

BTW, it's about 32*F here. Even if I sat with the throttle open a bit to warm up, I couldn't get the fan to kick on. Thermostat temperature stayed at about slightly below half no matter what.

 
Rep Power: 518

If it's cold and there's any breeze at all blowing through the radiator, the fan might never need to run. Run it or drive it long enough to open the thermostat a couple times and get the bottom rad hose warm.

The screw IS for idle adjustment.
It's for BASE idle. It controls (manually preset) an air passage around the closed throttle blade.

The IAC does the rest of the controlling as told by the ECM, so if you don't have it in the right mode you won't notice any difference because the ECM is still controlling the IAC to compensate over whatever you do to the screw.
You can hear the suction change as one or the other opens or closes.


I see 2 holes in the pic, one leads to the IAC and the other leads to the screw.

On a hot engine: Cover up the one for the IAC with your finger to seal off that passage and adjust big screw to about 600 RPM or so.
Do an idle relearn then see how it runs on a cold start.

 
Rep Power: 192

If I cover the hole for the IAC the engine stalls.

 
Rep Power: 518

I think computer controls hot idle RPM in neutral or park to about 700-750 RPM
Base idle should be just a little below that, 600-650.

 
Rep Power: 518

OPen the screw a couple turns and recheck

If you can't get any idle speed that way you may need to clean out the throttle body/blade/bore and passages for the screw.

 
Rep Power: 192

OK, I'll try that.
In the meantime, my thermostat temperature will be at zero when I start the car and I'll see it raise to slightly below half. It will stay here even on a super hot day. I guess we can assume the thermostat is still working?
I'm just paranoid now because I couldn't get the fan to turn on at all, and I saw steam coming out of the radiator. Apparently I have a leak as when I squeeze the upper rad hose I can see coolant come out just above the radiator.
I guess that's where my coolant is going, when it gets hot it escapes.

 
Rep Power: 192

I jumped the fan, and it did turn on, maybe because it's just so cold outside.

Thanks for your help ezone, much appreciated.
I'm going to adjust that valve now, and replace the rad and check thermostat while I'm at it.

That fluctuating idle which sometimes occurs seems to still be a mystery. Is there anything I should maybe replace? Perhaps IAC unit?

 
Rep Power: 518

Yes......or at least it isn't stuck closed.

It doesn't take much breeze to negate the need to run the fan.

Eeeyeah that needs fixed.

That RPM was changing far slower than I was expecting to see, It doesn't look real worrisome in the video but you say it does it a lot more or worse?....

I would first do and clean and adjust as discussed above, do the ECM reset and idle relearn, then see how it goes.

 
Rep Power: 192

Great. I adjusted the screw and found that when I plugged the hole to get 650RPM, my hot idle was about 1200RPM.
Then I tightened it two turns and the hot idle sat at 750RPM and when blocked was about 350RPM. I then gave it a full turn to make it in between and left it at that.

Denso aftermarket would be OK for the radiator?

 
Rep Power: 518

Gotta do the relearn after making changes.

Try it and see. Do the relearn though.
Sure.

 
Rep Power: 192

The colder the outside weather, when it does do the surging at cold start up, the worse it is.

Maybe I should replace the IAC, it seems when I was plugging the hole it would probably be the only device which would cause the RPM's to fluctuate.

Looks like new is $300, aftermarket is $170. Maybe I can find a used one to try out.
EDIT: Looks like Ebay has some super cheap ones for around $40, I should just get one of those and see if it does affect my start-up idle condition.

I disconnected the "back up" fuse and will relearn, see how it goes, thanks again!

 
Rep Power: 518

The engine needs more air to stay running while it's cold and it needs to run at higher RPM to speed warmup so the colder it is the higher the RPM will be, I'd totally expect that.

What happens if you disconnect the wiring from it then see what it does after cold start? (It's supposed to contain the FITV in that fat section where the coolant runs through it)...IDK, just thinking out loud and wondering/experimenting. I know it would set a CEL and code, but will it still fluctuate?

See what it does after relearn first.

 
Rep Power: 192

Just wanted to provide an update.
Fingers crossed, but everything seems to be running just fine. No fluctuating at idle AT ALL and overall response of the vehicle feels great.

I had taken the TB apart, and cleaned IACV, cleaned the air bypass screw and adjusted it (sorta, I guess, to what I felt seemed right, lol), then reset ECU and relearn idle.

Now, I just have to wait for IACV gasket and replace rad, which should be no problem. I'd also like to install a block heater as well while I'm at it, since I daily this hatchback and live in Canada.

I'll re-update if anything changes, thanks again for your help!
I'd like to try and make this last forever, since I don't like much of anything new from Honda.