I recently picked up a 2002 f4i with 24k miles. It’s got a flashed ecu, gutted cat, and yoshi slip on. It tends to idle high at 2,500 rpm. I’ve got the idle screw all the way to the left. Cold start it idles at around 4k. I checked for vacuum leaks, stuck cables, and replaced spark plugs. I have a feeling it’s the ecu, but sometimes it will drop down to the normal 1,500 rpm. When it does, it backfires at idle. Under power, it’s super smooth and doesn’t bog. The FI light is on, but I haven’t checked the code yet. Y’all think it’s just the flash on the ecu or something else? Thanks

 

I’d suggest that your best first step isn’t asking the internet what we guess is wrong!