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Low idle problem.

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4K views 8 replies 4 participants last post by  f250  
F
#1 ·
I have had a low idle problem for months.Runs fine above idle. The car starts then stalls or drops to 300rpm when cold. When warm it will idle at 700rpm in park but drops to 300 in drive or when the eas pump is on. I thought it was a stepper motor problem but got no codes till it does not start and then only an 02 sensor out of range but there is black smoke out the pipe by then so its flooded. I broke the stepper motor for the winter so it would start thinking it was over fueling with stepper motor closed so I stuck it open. When I put a new stepper motor in it looked like the old one had moved all the way to closed. The problem is still there with a new IAC.

Thinking. The spark plugs are always white. The motor runs fine above idle. A manifold leak between the IAC and 02 sensors should not make the idle change as the ecu will adjust with the IAC closed and more fuel unless the leak is to big then it should give a code. A leak between the MAF and IAC would act the same but when the IAC closes it would choke the the motor.
 
A
#3 ·
I think you ae a bit confused with this,if the plugs are always white and the idle speed dies under load then its running so weak it is not making enough power to maintain the target speed.If the iacv is showing 0 at idle then there is too much idle air WITHOUT any added through the iacv passage.Idle air and mixture strength are two different things.What are your oxygen sensors doing ? Are your coolant,fuel and ambient air temp sensors reading correctly ?
The iacv can only control idle speed if the engine is running well and developing power.
 
F
#4 ·
allyv8 said:
I think you ae a bit confused with this,if the plugs are always white and the idle speed dies under load then its running so weak it is not making enough power to maintain the target speed.If the iacv is showing 0 at idle then there is too much idle air WITHOUT any added through the iacv passage.Idle air and mixture strength are two different things.What are your oxygen sensors doing ? Are your coolant,fuel and ambient air temp sensors reading correctly ?
The iacv can only control idle speed if the engine is running well and developing power.
Click to expand...
I though I would need to change the IACV passage to get the idle right but now think I need to fix what the problem is and not make any adjustments. Yes it is acting like to much idle air that I think is a manifold leak but that would only be if there is a fuel trim for idle that is different from regular running or the 02 sensors would correct for it. All 02 sensors are switching and all sensors look normal.

I also know the previous owner had the same problem for a year and have not looked yet to see if something was adjusted wrong as I just put the new IAC in.
 
F
#5 ·
And now I chase my tail. Hooked up fm sv today and the stepper is working as it should. Cold start 76 steps and warm 34 steps. the long term steps were at 0 and if I push the throttle and release it would drop to 300rpm then back to 700. I found in engine setup it was set for a manual trans and the long term idle was 13 steps so I set it to auto and wrote the settings. Now it idles at 700 with everything on and in drive.

I also noticed the intake temp showed -17C when cold but it is 3C outside and went to 13C when warm. I had only looked at intake temp when warm and siting at an idle with it being within a few degrees of outside thought it was Ok. This could be why its running lean.
 
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