I did a search and read many threads but wasn't able to find my exact problem.

Background:
CEL was on for EGR and poor secondary O2 performance. Determined my cat had failed, so I replaced my exhaust with a Megan header and Magnaflow cat and cat back. I also cleaned the EGR ports on the intake manifold and on the cover plate. Since then my car has been idling very low and roughly, increasingly so as it warms up. At normal operating temperature it will idle around 100rpm and frequently stall.

What I've tried:
Based on searching this site and others, it was looking like my IACV was the culprit. I pulled it off and sure enough the screen was clogged and the interior coated in carbon deposits. I thoroughly cleaned it, put it back together, and it ran like a dream. For about 15 minutes...

Problem:
Now it's back to its low idle, stalling ways. Pulled the IACV again and it's still relatively clean. The screen is clean, although there might be more carbon deposits in the body from the short time it was running (hard to tell if I just missed a spot, or if it's new deposits).

My question is twofold:
First, what causes the IACV to become clogged? I expect it to be dirty after 196k but the cleaning seemed to work, until it didn't. If I place my hand on it, I can feel the IACV motor humming when the ignition is on - is that normal? I suppose it's possible the IACV might actually be faulty.

Second, if not the IACV then what else might be causing the low idle and stalling? I'd rather spend more time on diagnosis rather than $180 on a new IACV that doesn't fix the problem.

 

Check the passages where the IACV connects. If there was a lot of carbon in the IACV you may want to take the throttle body off and clean it thoroughly from the back.

 

I cleaned the throttle body - there wasn't as much carbon as I would have expected given how much was in the IACV. It didn't make any difference - at cold start it idles okay-ish, but after warming up it drops down to the point of stalling. It has plenty of power when I open up the throttle; the only problem appears to be the low idle.

I'm very curious about the timing of this problem. It wasn't an issue until I replaced the exhaust system and cleaned the EGR ports, which one would think would make the engine run better. Instead it's running worse than when the CEL was on.

 

An EGR valve stuck open will cause stalling at idle. Make sure the EGR valve moves freely. The ECU is supposed to close it at idle. So with the passages clogged up it was working like the valve was closed all the time, which is good for idling but bad for smog.

 

Heck if I can get the EGR valve off. Looks like I need to pick up a 12mm crows foot - for some strange reason my set goes from 11-18mm but skips 12mm. WTH?

Is there a way to clean the EGR without taking it off? Seafoam treatment perhaps?

 

I finally got back to this project.

Drove the car out to the middle of the potato fields and did the SeaFoam treatment. It's idling much better, but is still off a tad. I'm going to see if another treatment does the trick and I can avoid pulling the EGR valve.