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Can the IAC Cause Stalling?

8

88XJSport

NAXJA Forum User
Location
Michigan
Ive always heard that the IAC causes high idle when the sensor sticks and goes bad, but does it also contribute to rough idle and intermittent stalling? It stalls once a day...stutters once and dies in traffic. The TB is clean, and the IAC is clean too. TPS is fairly new and adjusted accordingly.

88 4.0, AW4 231. 189k

Thanks.
 
Yes it can. Replace it and if that don't work, just take it back and go from there. I bet it is the IAC though.
 
It can when the engine is cold. The IAC opens a bypass around the throttle plate to increase the air going into the engine when cold. The ECU then pumps more fuel to compensate for the added air which raises the idle speed.

As the engine warms, the ECU extends the pintle to close off the bypass.

The high idle usually occurs when the pintle or the seat is dirty and the passage does not close off completely. Of course, the IAC could be faulty as well but generally a good cleaning is the first step.

So if the pintle does not retract and open the bypass a bit, you could have a low idle that could result in stalling. Could also be due to buildup in the passage. I'd try a good cleaning here as a first step as well.

Once warm, does it idle OK?
 
Saudade said:
Once warm, does it idle OK?
Click to expand...

Once warm the idle is marginal. It slightly chugs at warm idle aometimes...then once a day, it will stutter once, and die. Restarts right away, but the idle is at 2800 rpm for about 2 seconds. TB and IAC were cleaned this past fall...
 
Start with the basics like cap, rotor, wires, plugs, air filter. I am not saying replace them, just check them out. You can tell a lot looking at a spark plug.
 
Saudade said:
As the engine warms, the ECU extends the pintle to close off the bypass.

The high idle usually occurs when the pintle or the seat is dirty and the passage does not close off completely.
Click to expand...

Not trying to contradict here, just trying to learn --

Doesn't the IAC also let the intake air through for warm idle. I though it controlled idle at all temperatures and the throttle actually closed? :confused1
 
XJPioneer88 said:
*Raises Hand*While we are on the general subject, How would you or anyone go about a cleaning on this?
Click to expand...

Here you go....

Cleaning the IAC:
1. Remove the IAC with a torx 15 driver (2 bolts)
2. Gently wiggle out the IAC from the throttle body
3. Clean the IAC with throttle body cleaner (not carburetor cleaner ) Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle as it is fragile and you can damage it pretty easily
4. Also clean where the IAC seats in the throttle body with the same throttle body cleaner
5. Consider cleaning the entire throttle body itself as long as you’re at it
6. Reinstall IAC and check idle quality
 
The Renix manual doesn't say it closes. It says it just restricts. Under the right condition, I guess the passageway could still be slightly open. On my 88, I checked it once when I finished cleaning it by covering the opening with no change to idle. There was no sign of suction. It was a warm summer day and up to full temp.

XJPioneer88, I use some throttle body cleaner and some small bottle brushes. Spray, scrub, spray, repeat. With the air inlet tube off you can look down the passage and see the end of the IAC. I could watch the pintle extend and retract as it was started and shut down.
 
When my IAC went bad the engine appeared not to try to idle at all. It ran fine with your foot on the gas but if you took it off it just reved all the way down and shut off. A replacement fixed that. I didn't try cleaning it, I just bought a new one.
 
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