Rough idle, intermittent CEL

[spencp86]

im running a 3.2 engine (obdi) with m50 swap, 3.5 HFM, turner motorsport chip. Car ran great until about a week after doing the 3.5 hfm and TMS chip, i started it to a rough idle and CEL. Cel disappeared and didnt reappear until tonight (disappeared soon after that); idle has still been fairly rough, bouncing between about 500 rpm and 800 rpm, but only intermittently. Also notice large loss in power when the engine is acting up. Tends to get better after warming up. My first instinct would say o2 sensor, but i cant get a CEL check because the light is basically never on. Anyone had an experience like this? after searching nothing quite fit my description...is there a common cause of an intermittent CEL like this?

[bmwdirtracer]

The code is stored in the dme, whether or not the CEL is lit. Check the codes. Likely an intake / vacuum leak, though; rubber hoses open or close gaps depending on temps and loadings.