I have a 2005 Tiburon GT v6 and put an Injen SRI on it back in July. A couple months ago my CEL started coming on when on long trips. If I drive for a couple hours, turn the engine off for a quick stop and then start it back up, the CEL comes on immediately. If I clear the ECU, it's good until I have the same conditions as I just mentioned. The codes are for system running too lean bank 1 & 2. Some things I've tried so far are replacing the plugs and wires with NGK ones, checking the intake connections, and cleaning the MAF. I'm not sure if this is something that's just a quirk of the intake or if something is actually wrong. It's weird that it only happens under the conditions I mentioned above. If I'm driving around town normally, the CEL doesn't come on at all. Has anyone else had a similar problem or know what to do to fix it? I have all the stats from the OBD2 reader if that would help too.

 

Put the factory air box back on test drive..

Hyundai has had a few instance where wrong air box parts used and lean codes set, so inlet prior to MAF very well could be your problem.

Feel free to post your Freeze Frame data..