Can' control Low Idle code
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Senior User
Joined: Jun 2004
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Can' control Low Idle code
I don't remember what code number it is, but I keep getting a can not control low idle. I just replaced the TPS but I did not go with the OEM so perhaps that is the problem. If i unplug the IAC it has a nice low idle, I am half tempted to leave it unplugged but that would just annoy me. I want it running right. Any help would be appreciated.
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Joined: Sep 2004
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If you are getting code 411 in the KOER test, it happens under the following circumstances:
The ECM commands the IAC to a low-flow position during KOER, and then checks the speed of the engine by observing the PIP signal. If the engine speed is higher than it "should" be for that IAC position, it sets code 411.
Since the ECM directly controls idle speed, it will do "whatever it has to" to try to get to the appropriate RPM outside of the KEOR test. It may move the IAC to a less open setting than during the low-flow test, and may thereby achieve a reasonable RPM. Under these circumstances, normal driving is unaffected but you will get code 411 during the test because the ECM feels it has to try too hard.
Alternatively, the problem may be bad enough that the idle speed is too fast all the time, and the ECM is unable to slow it down enough within the test or outside of the test.
Reasons this happen include:
1) IAC dirty and unable to close far enough
2) IAC wiring problem or motor not working
3) vacuum leaks
4) Timing too far advanced
5) Throttle blades not closing far enough, due to dirt or improper stop setting
6) PCV valve not sufficiently restricting airflow (another form of vacuum leak)
The E40D versions of the F-series (at least the 302 V8) do not have an idle speed adjustment. The stop screw on the throttle blade is speced to a specific setting and you aren't supposed to fiddle with it. If the ECM is complaining about idle speed, you have to look elsewhere and fix the problem.
In other versions, there is a procedure to set the throttle blades appropriately at the end of the KOER test, and performing this may compansate for a sticking IAC, vaccuum leak, or whatever to "fix" code 411.
Ironically, I dealt with exactly this same fault this afternoon, and it turned out to be a dirty IAC. It comes off easily (two bolts). You then take off the IAC motor (two more screws), and clean only the valve portion. Mine didn't look all that bad, but a session with some "Engine Brite" and a solvent rinse (together with manually moving and spinning the plunger) seems to have cured the problem. No more code 411.
The ECM commands the IAC to a low-flow position during KOER, and then checks the speed of the engine by observing the PIP signal. If the engine speed is higher than it "should" be for that IAC position, it sets code 411.
Since the ECM directly controls idle speed, it will do "whatever it has to" to try to get to the appropriate RPM outside of the KEOR test. It may move the IAC to a less open setting than during the low-flow test, and may thereby achieve a reasonable RPM. Under these circumstances, normal driving is unaffected but you will get code 411 during the test because the ECM feels it has to try too hard.
Alternatively, the problem may be bad enough that the idle speed is too fast all the time, and the ECM is unable to slow it down enough within the test or outside of the test.
Reasons this happen include:
1) IAC dirty and unable to close far enough
2) IAC wiring problem or motor not working
3) vacuum leaks
4) Timing too far advanced
5) Throttle blades not closing far enough, due to dirt or improper stop setting
6) PCV valve not sufficiently restricting airflow (another form of vacuum leak)
The E40D versions of the F-series (at least the 302 V8) do not have an idle speed adjustment. The stop screw on the throttle blade is speced to a specific setting and you aren't supposed to fiddle with it. If the ECM is complaining about idle speed, you have to look elsewhere and fix the problem.
In other versions, there is a procedure to set the throttle blades appropriately at the end of the KOER test, and performing this may compansate for a sticking IAC, vaccuum leak, or whatever to "fix" code 411.
Ironically, I dealt with exactly this same fault this afternoon, and it turned out to be a dirty IAC. It comes off easily (two bolts). You then take off the IAC motor (two more screws), and clean only the valve portion. Mine didn't look all that bad, but a session with some "Engine Brite" and a solvent rinse (together with manually moving and spinning the plunger) seems to have cured the problem. No more code 411.
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Senior User
Joined: Jun 2004
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Thanks so much for the info. I will play with it later this week. I am headed out of town for the week so no time now. That was a great wealth of info. This site is awesome for learning about fords.
