surging idle gone but....

[Haley]

So a 'friend' of mine (who is a mechanic), was driving my car last night and heard the idle surging at a stop. He said it was usually the IAC motor and asked if I had tried running without the iac hooked up. I said no, so we decided to give it a shot. He unplugged it, and the surging idle stopped. The car runs good, and there is no cel coming on.
But....isn't there a vac hose connected to the back of the iac? How is this going to affect the engine....if at all?

[Inodoro Pereyra]

You can run the engine without the IAC. The IAC doesn't work with vacuum. It's just a valve that lets some air bypass the butterfly valve when it's closed (when your engine is idling) when needed.
The only problems you can have when unplugging the IAC is your idle going down (instead of up) when you use your A/C, or when you apply any big load to the engine, and the engine taking a little longer to warm up when you start it.
Either way, if you need to go through emissions inspections, you probably won't pass them without your IAC,.

[wytbishop]

I have a very small leak in my coooking system that I have not been able to completely stop because I'm not willing to remove my heater core. Anyway when the coolant level gets low the IAC sensor is no longer submerged in the hot coolant (because it is the highest point in the system) and the ECU gets confused as to the temperature...and the idle gets wierd.

Fill your coolant like this...

-with the engine off and cold remove the engine filler cap and fill it to the top.
-leave the cap off and start the engine. The water pump will circulate the bubbles out and the coolant level will go down. Continue adding until the level stops going down. Should take less than a minute.
-stop the engine and remove the rad cap. If there is an air pocket it will be right at the top. With both caps off the coolant level in the rad will automatically rise (because it's lower than the engine fill cap). So basically just remove the rad cap and replace it when the level comes up...just takes a few seconds.
-top up the engine side if necessary and replace the cap.
-fill the overflow tank to the cold line.

When the engine's cold there will not be much coolant in the overflow. As it heats up the coolant expands and flows in. When it cools again the coolant contracts and is sucked back up from the overflow. There should always be some coolant in the overflow. If it's bone dry a couple days later that's a good indication that you have a leak. In my case the coolant leaks very slightly from the heater core intake hose when the system pressures up and then when the engine cools it sucks all the coolant out of the reservoir. After a week - 10 days I wind up a little low and the idle starts to act up.