iacv prob

n01d3x

New Member
My car failed noxduring CA smog. I did a tune up and changes the fuel filter. I also cleaned the iacv and replaced the gasket. Now after the engine is warmed it idles up and down constantly. It didn't do this before. If I unplug the wires from the iacv the car idles fine. The idle screw was all the way tightened. I lossened it and nothing changed. I left it just barely backed off. Its a 93 with a 15b7.
 

khmernese

New Member
You have to do the idle learn process when you clean an iacv
 


n01d3x

New Member
I followed the procedure for the idle relearn process. I drove it around for about 50 miles, on and off freeway. Nothing changed, does this normally take awhile? Also, it only idle surges in park or neutral. I think the previous owner tightened the idle set screw all the way just to hide a bad idle problem. How much should I back this off to attempt to make it right? How can I tell if the the IACV is working right?
 


khmernese

New Member
take a volt meter to it to check if its working correctly.

DO NOT adjust the idle screw under any circumstances, it is set at the factory and that is the reason it was sealed in the first place. If you find that the seal has been broken then you might turn the screw out a little to see if that helps the idle but only enough to try and bring it back to where it was before it was adjusted in the first place.


IDLE LEARN PROCEDURE:

Take off the battery cables and connect them back together after 10 min and then perform the base idle relearn procedure below:

Make sure all electronics are off. As in radio, a/c heat, open doors are all off/closed.

Turn the ignition switch ON (II), and wait for 2 seconds.

Start the engine. Hold the engine speed at 3,000 rpm without load (in Park or neutral) until the radiator fan comes on, or until the engine coolant temperature reaches 194 ºF (90 ºC).

Let the engine idle for about 6-10 minutes with the throttle fully closed. So dont do anything for 6-10 min.

If the radiator fan comes on, do not include its running time in the 5 minutes.

Turn car off and then back on again. Go drive around.

Eventually the ecu will learn everything by driving for a couple hundred miles if you don't reset it.
 

codeman76

New Member
To adjust your idle speed warm the car to normal operating temp till the radiator fan kicks on at least once. Turn the car off and unplug the electrical connector from the IACV. Restart the car hold the idle at about 1000 rpm until it idles on its own. Then go tighten the idle adjusting screw in till the car starts to die then start backing it off again until the idle feels right. Keep checking your rpm gauge to see what your idol is at. Once you get it right kill the car reconnect the electrical connector back on the IACV. Then pull your 7.5A back up fuse in the fuse box under the hood for at least 3 minutes. Reinstall the fuse and start it up and let it idol till the radiator fan kicks on twice. then go for a 20 minute drive to reset the ecu. Give it a couple WOT while your driving.
 

n01d3x

New Member
After I do the relearn should there be a difference in idle? I followed the process and after about and hours drive it has changed at all.
 

RonJ

Banned
The IACV is unlikely to have anything to do with high NOx emissions. For the hunting idle problem, start by bleeding the cooling system.

In general, engines produce high NOx if they are running lean or too hot. Is the temp gauge reading abnormally high? You replaced the fuel filter, but did you measure the fuel pressure and test the FPR? Are the fuel injectors clogged? Also, have you checked the ignition timing? Is it set to spec?
 

n01d3x

New Member
The car was stuttering off the line and I believe it was you that told me that could be a fuel filter and could be related to the high nox. After replacing the filter the stutter problem is gone and the car runs a lot better while in gear. I think this along with the cat not being warm attributed to the high nox. I have not measured fuel pressure or tested FPR.

I checked the ignition timing with the IACV unplugged. It was off a little so I put it in spec. Seemed to run a little smoother but not much of a difference. Checking the timing is impossible with the IACV plugged in because of the idle hunting. It's weird that the idle hunting only started once I removed and cleaned the IACV. Which would seem that there could be air the system. I bled it off with the bleed screw on the block, no air came out. My overflow tank has always been empty, I added coolant just above the low line.

The temp gauge never reads hot. I kind of think it may not being reading right and/or I have another problem with the coolant system. The fans rarely come on at idle or not. All of the hoses are hot after its warmed up. I am not sure but I think the fans came on quicker when I had the IACV unplugged. I guess I could test this further but I wasn't sure if running it with the IACV unplugged for too long would hurt anything. I can tell that the idle hunting starts after its warmed up, and I can leave it that way for 20 minutes or longer without the fans kicking on.

I am also concerned with the idle screw situation. The paint was already cleaned away from it and it was tightened all the way down. I backed it off just a tiny bit, but have not unplugged the IACV and tried to adjust it because I don't think that is this specific problem because it wasn't idle hunting before I removed and cleaned the IACV.

edit: If it is just that it needs to relearn idle would resetting the ecu and driving it awhile how a difference? I have put about 150 miles on since resetting and it has not changed at all.
 
Last edited:

RonJ

Banned
Any CEL codes?

----------------
Start here:

Bleeding the cooling system may take 20-30 minutes.

1) Park the car on an inclined driveway with the front end higher than the rear.

2) Push the dash heater lever/knob to MAX heat.

3) Follow the directions in the diagram below (hint: the bleed bolt is located where the upper radiator hose connects to the engine):



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

If bleeding the cooling system eliminates the hunting idle, then adjust the ignition timing to spec as described in the service manual.

-----------------------
If the idle speed still hunts, then do this:

Idle problem diagnosis
Warm the engine up. Remove the air intake system. Start the engine. Inside the throttle body, there are two holes/ports. One leads to the IACV and the other to the FITV. One at a time, cover each hole with your finger. Does the idle speed drop to a low or normal speed when one of these holes is covered?
__________________
 

codeman76

New Member
When you check your ignition timing you do not unplug the IACV. When you check your ignition timing you need to jump your 2 wire service connector with a paper clip.
 

n01d3x

New Member
No CEL light, but I haven't actually attempted to pull any codes. I will check for codes after I bleed the coolant as described.

I did jump the service connector when I checked the ignition timing, but had to unplug the IACV because that's the only thing that would stop the idle hunting. It was impossible to check timing with idle hunting going on.
 

RonJ

Banned
n01d3x said:
I did jump the service connector when I checked the ignition timing, but had to unplug the IACV because that's the only thing that would stop the idle hunting. It was impossible to check timing with idle hunting going on.
Click to expand...
The engine must be idling to spec in order to set the ignition timing correctly.
 

n01d3x

New Member
The CEL comes on at Ignition II I believe its called. It goes off right away. So I think its working.
 

n01d3x

New Member
Well I bled the system multiple times. No air ever came out but I kept letting coolant come out of the bleeder and then refilling just to be sure. The fan never kicked on once. I let it sit about 5-10 minutes to warmed up. I can tell its warm because as soon as it does warm up the idle hunting starts. Its cold and rainy outside so I dont know if thats why the fan never kicks on. The temp gauge never reads even half way. I'm going to try covering the intake holes in a bit.

Just to be sure, this wouldnt just be the ecu trying to relearn idle would it?
 

n01d3x

New Member
Ok, I took the intake off. Covering the bottom hole has no affect. Covering the top hole it idles normal or maybe a little low, either way the hunting goes away.
 

n01d3x

New Member
Ok, I think I may have found the problem. Covering the top hole, which is the IACV hole I believe, fixed the idle hunting. I also found that if I push the top of the butterfly valve, closing it tight, the problem goes away as well. I'm going to try to clean that area as best as possible.
 

n01d3x

New Member
I took the TB off and it was horrible inside. I think when I cleaned the IACV and put it back on it sucked the loose crap into the TB causing the butterfly not to close all the way. I cleaned the TB real well and put it back on. Hunting idle is gone, for now at least. I put the ignition timing in spec and all is well. I'm not sure if changing the fuel filter, tune up and ignition timing adjustment will help me pass smog, but we shall see. I think I'm going to run another round of cleaner in the the tank before though.
 
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