I am near my wits end. I got a 04 TSX in the shop with 85k on the clock. Engine mods are just a Comptech Ice Box. Anyways, The issue that I can't figure out is the idle issue the car is having. I'm getting misfire codes on cyl 1, 3, 4 and random misfire. I readjusted the valve lash, new NGK iridium plugs and I'm getting spark from the coil packs. I'm suspecting it might be the PCV valve, but it seems to be working properly. If its not the PCV valve, then I'm pretty much out of ideas. So, I'm tossing it up to you guys. Toss out some ideas.

 

Have the mechanic (if he isn't already doing so) check the vacuum lines throughout the engine bay. It sounds like something more broad than a cylinder-specific problem (like a spark plug would be), so maybe the timing is slightly off, or a vacuum line is partially disconnected, or as you said, PCV might be on its way out. There are usually fairly easy checks for these, too.

For the PCV, with the car running, pinch the hose in front of the pcv valve with pliers (with tubing on them to not damage the vacuum hose). If you hear a clicking noise, the PCV should be fine.

For timing, a mechanic can use a timing light (I believe) to check this, but you'd probably get a CEL with a specific code if it were out more than a few degrees, though I'm not certain on that.

Is it sitting at a dealership with well-trained mechanics, or at a shady-tree mechanic with no real concept of newer cars with a ton of electronic gadgetry and diagnostic systems?

 

I'm the tech on this car in my workshop. I'm a former certified factory trained tech. I checked pretty much all of the vacuum hoses and really couldn't find anything. Ignition timing (per OBD-II scanner) is where it should be. Breather tube is clear, booster is working fine. So, yeah.