Hello, to whomever is reading this. I "had" several small problems with my S4....
1. Rough idle (not eratic, just rough)
2. 3800
3. Extra rich (lawn mower rich)

So after reading here I decided to go back to the stock setup, with a K&N drop in, from my standard K&N cone right on the AFS.
After install and a good drive, everything changed. It idles smooth, no hesitations @ 3800..... It even smells different. (noticable leaning effect)

Am I crazy, lucky, or what??

 

Chances are you had an air leak somewhere. Is it T2 or N/A?

 

A vac leak would cause it to run leaner at idle, not richer like he is describing. Also, everything he changed is before the AFM, so a leak wouldn't do anything to how the car runs.

As for why it runs better, I have no idea. Maybe the cone filter was really clogged?

 

I'd say crazy but I don't know you very well at all.

 

hmm, Sidewayz is right. Could it be the AFM not being level? If it were tilted the right way and was sitting open, would it not tell the computer that he's at high airflow and cause it to run very rich to compensate for the non-existent mass amounts of air being inducted?

 

NA...Years ago when I changed over to the cone, I made sure to level the AFM as it sat before. I recharged the cone myself ,annually. No leaks... have done the propane test many times..

 

So you had that filter on there for a good while before it started acting up? Have you driven through puddles of water that could have gotten in to the filter? Wet filter equals bad filter.

 

Nah...I had it protected for the most part. The problems came on slowly over about 2 years. First the idle, then months later the hesitation,smell, etc. I inspected the filter every other month. And I dont drive it in the rain.

Over the last year I've replaced and worked on all the normal sources for the previously mentioned problems.
1. Regrounding thanks to Aaron's write up
2. New TPS
3. Remanufactured ECU
4. New ACV system, and pump.
5. Tested all remaining sensors
6. Leak tested everything
7. Tested secondaries , they were fine. Primaries also fine.
8. Compression tested, just as it should be for a 25,000 mile engine.
None of those "fixes" fixed anything. Im at a loss here.