Originally posted by bones:
Where and what is the IAC?



First, if you're getting EGR codes, the IAC is likely not your problem. You should search this site for a test of the EGR valve - it was described here recently. The EGR valve is usually fine & the DPFE is a more common failure.

Now get this: The most common problem with EGR codes requires only a simple TB cleaning to resolve. Its a do-it-yourself easy task that requires the investment of $4 for a gasket, $3 for some TB cleaner, and an hour or so of time.

NOW TO ANSWER YOUR QUESTION:

IAC = Idle Air Control valve
It is a cylinder shaped thingy located at the rear of the Upper Intake Manifold (UIM) on the driver side. It will have and electrial connector & one 3/4" hose running to the intake accordian tube. There are two bolts that hold it in place. Upper bolt is easy to see & work with. The lower has access issues because it is close to the fire wall & some eletrical/plumbing stuff. You will usually go at that one blind.

It controls the air flow into the engine to maintain idle. Sometimes they get a bit gummed up & stick:

Closed: car won't start or will only run if the throttle is pressed slightly.
Open: idle won't come down to normal level.

Occasionally, you might get an idle that hunts or surges up & down - which is usually an indicator that the IAC needs a good clean & lube.

On rare occasion, they fail.

Must be that jumbly-wumbly thing happening again.