Long threads suck, I will be concise.

I got a CEL. My idle shook, a little. Time went by...

The idle started to shake harder, sputtered at the bottom, and the engine died frequently (in mornings).

Took the car to mechanic. Valve Adjustment to extremely loose air valves. CEL went off. But what caused those air valves to loosen up so much?

Few weeks later the idle starts to fluctuate wildly (under 1000rpms to above 2000rpms) at stops. When it doesn't fluctuate, hard idle. No engine dying, yet. I'm pissed.

Mechanics only suggested the band aid, I needed to find the problem. Felt like my car just wasn't get air properly.

Removed wheel and inspected my AEM V2 CAI. Here is where to pay attention: there is a rubber plug near the bottom plugging up a hole near the filter (god knows why it's there, but you cannot see it unless you take off wheel and remove mud flaps). My plug was torn, the hole was virtually open. My car was getting proper air flow, if any.

Got pissed off at AEM. Removed the whole CAI V2 extension and put an air filter on the short pipe.

Car runs beautifully. Sounds throatier, accelerates with vigor... it even handles MUCH better because I have proper accel/decel in the turns creating the friction and grip I need. After a year + of owning my S2000 (the AEM V2 CIA was put on shortly after I got it) I finally understand why this car is so amazing. I almost traded it in before I fixed this problem... thank god I didn't.

I still have the V2 extension with the plug, let me know if you want pics.

 

What is an air valve?

 

I think that plug is a water bypass valve - if you get water into the AEM intake, you can pop that valve off to remove the water.

Btw, when you made the intake shorter, you may have made it a hot air intake...so you should look at where its picking up air from!