2006 Mustang V6 backfire or popping in intake. Any ideas how to find the issue? I don't see any vacuum leaks, all plug wires are on tight. could it be a valve, the EGR (which is new), the MAF, to much oil? It starts and runs good. When you let off throttle it pops a little in the intake. When you shut it off its loud in the intake and almost sounds like a grinding and popping together. I don't have a scope to run diagnostics. No engine lite and no codes.