Need help: excessive idle popping

Hi yall,

I recently built an e90 with n54 engine, maxxecu standalone ecu with port injection (bosch 750cc) and single turbo.

After I dialed in the idle, it starts to pop constantly, my idle is rather smooth, but i do see lambda being kind of unstable, when it pops, lambda will jump from 0.85 to 1.00 and back. My mechanic found that spark plug is pitch black which shouldn't be happening considering the car hasn't been driven since spark plug change. Ignition was based on idle error, it stayed at 10-15 degrees so it should be advanced enough to prevent pop from happening. Just to clarify, the popping is from the exhaust, not from the engine bay (at least for now), and it's pretty loud. Also the fuel trim jumped from 5% to 30% for some reason, I will try to log it tomorrow.

I will upload my tune files after I got home, the VE table was messy since I am only tuning the idle part, my apologies in advance.

For some reason, this forum doesn't like maxxecu save files, it shows i'm trying to upload null file, I have to make it into a zip file.

For now the pcv hose was open so it was VTA, but I don't think that will cause this.

Has anyone encountered this issue before? I really appreciate everyone's help, cheers guys.

Intake leaks, cracks in exhaust manifold, marginal coil, trigger errors, intermittent coil or injector wiring. These problems are hard to find. Make sure the ECU isn't reporting any errors (like trigger errors) that might provide a hint.

First step is to try an determine if this happens just on one cylinder. I suggest disconnecting the injector for one cylinder at a time. Engine will misfire, but see if the exhaust poppoing still exists -- If that identifies the cylinder then I would look for coil / injector wiring issues (or cracked header) on the one cylinder that unplugging caused the popping to stop.

One more cause -- make sure you aren't low on fuel and getting low fuel pressure, or air in your fuel delivery.

Thanks David! This car got a lot of aftermarket parts at once, I will start by checking ignition and injectors, hopefully I can pin point what exactly is the issue, too bad my single turbo header only got one lambda on the downpipe, if it was stock dual bank it might be easier :(