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First post here so thanks in advance for any help. Before I state anything about my question, I will say that "yes" I read the sticky about idle issues. I bought a 2004 Honda Civic EX, auto about two weeks ago real cheap. Guy told me he thought it might need a headgasket because it smokes but that he disclosed he knows nothing about cars. He also stated that they paid a hefty amount of cash to a Honda dealer to replace a headgasket in January and he believes his daughter overfilled it with oil and maybe that is why it is smoking.. I went to look at the car in the the rain and he said it had been sitting for about six months and the battery was extremely dead. I bought it without hearing it run because it was so cheap I figured a junk yard would pay me what I paid for the car if I needed to get back out of it. I went back with some jumper cables and it fired right up. It was blowing some blue smoke and it idled pretty high. I put about 100 miles on the car and the blue smoke seems to have cleared up completely but the idle is still almost right at 2000 rpms. I was thinking that maybe it needed to relearn the idle since it sat with a dead battery for several months. I tried the relearn procedure a couple of times. No luck. I also pulled the PCV valve and checked for what seems like good operation. Cleaned it out with little carb cleaner and reinstalled. I have searched for vacuum leaks and have not found any. I pulled the IACV and cleaned it twice and reinstalled. No change. I found the hole in the throttle body that feeds the IACV and plugged it with my thumb while it was running and it then idles perfectly. I figured the IACV was stuck open. I went to the junkyard yesterday and picked up two used IACVs (in case I got a bad one) Neither of the junkyard IACVs made any change. If I plug that port of the throttle body with my thumb it idles perfectly with both of the junkyard parts too. I am convinced that it has something to do with the IACV since it idles right where it should when I plug that port in the throttle body. Is it possible that the ECU is not telling the IACV how to behave properly? How could I test that with a multimeter? I have 12 volts on the IACV middle connector pin with the ignition turned on. I have continuity to ground on the the pin that is supposed to go to ground. With the ignition turned to ON It seems like there is some continuity but with resistance between the signal wire (black/red) that goes to the ECU and the ground pin. I am not sure how that works. Does the signal wire feed voltage or create another ground to work the stepper motor? I am out of ideas on my own. Any advice is greatly appreciated.

 
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any engine codes? Is the engine light on? Does the code reader connect to the car?
Idle relearning - if battery was dead, the ECU forgot the idle already, no point in doing it

 
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There is no CEL on but I just put my scanner on it and it connected the ECU without issue. It showed a P0113- Intake Air Temperature Circuit High Input code even though there is no light on the dash. I tried pulling codes a week ago and it didn't show that code so that is new. Maybe helpful. I did let it run for a bit with the IAT sensor unplugged since the air box was off it while I was swapping out IACVs and letting the car idle while I tried them out.

 
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woups, the relearning is needed, though, since it forgot previous settings.

by experience, during the headgasket job, moving or unplugging sensors that have been in place for years makes then prone to start presenting issues after the job. Grease, oil gets into them too during the job. start plugging/unplugging them to see what happens

 
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I greatly appreciate your ideas. Sometimes it just takes a second brain to come up with solutions. I will try unplugging things and looking for changes in idle behavior to see what I info I can gather.

 
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Check the wiring and connector for the IAC, might have a broken wire or bent pin