MY 02 mini cooper s has a Long term fuel trim of 15.63% this seems a little concerning to me. I am also seeing a P2096 code for o2 sensor too lean(Bank 1 Sensor 2). My car has 500cc injectors, 15 percent pulley, dinan CAI, m2 performance header with cat delete, nvidia n1 catback exhaust, Vibrant j-Bend defouler(originally had the middle sized bung and tried the larger but no change), A tune from Jan using the MyGenius tool, and a step cooler quad tip ngk spark plugs. I noticed my idle seems to surge when at a stop for a minute, where it will almost stall. I've heard this is caused by the canister purge valve, but this doesnt seem to be a normal thing. Lastly, I know its somewhat typical for r53's to run rich, but my exhaust will blow black/grey smoke if I rev it, it also smells of fuel a LOT, and spits out wet black liquidy soot when warming up. if anyone has any ideas

 

Idle issues like you describe often point to a vacuum leak.

Your downstream O2 reading too lean seems to support that unmetered air is going through your engine. High fuel trim is the ECM (or whatever acronym for the engine control module MINI uses) adding fuel to correct the lean condition that O2 is reporting.

 

I've been focusing my efforts on trying to remedy my o2 sensor thinking it was due to the cat delete, But i think i may start looking into a vacuum leak. i fought with a vacuum leak issue before involving 2 hoses way below the throttle body, i could spray carb cleaner down there and the idle would fluctuate, but it was hard to pinpoint it. I worked at pushing the hoses all the way into their ports, but it is a very tight area. i also did a smoke test With a mason jar, baby oil, and some old socks and a fuel line to blow the fog into the intake. I was unable to find any leaks, but I've also heard you need to get a couple psi in there for some leaks. i think in the morning ill try to get to those fittings if possible to get a better look. Thanks for your help! ill post an update on my findings.