Cool info Stephen. However the plugs are defiantly not the problem. Those plus 4 plugs are what you get if you walked into a dealer. The part number is on real oem as the high performance plug. Ya you might get a lil better performance from an iridium plug (I don't race my X), but they don't last near as long.... I have plus 4 in 4 bimmers now with zero issues.

I had this problem and it was the plug gap... Seems that when I was inserting the plug into the spark plug hole some of the plugs fell out of the socket and messed up the gap... ( plug fell onto the end and closed the gap smaller than was specified) recheck the gap on the plugs for cylinders that have the misfire

I have the multi prongs in two of my BMW also. The 4.8is and the 3.0 seem to like the fine wire ones a little better IMHO. Both will provide long life 50K easy. I tend to replace them at 15 to 20 K in my vehicles as that tends to be every 3-5 years. For my M5 that would be every 10 years......

We used to see cars come in all the time at the shop with +4's in them... always ran better after replacing with OEM single electrode or NGK Iridiums. I'm guessing the +4's are listed as the performance plug because of a deal with Bosch and BMW.

Just my experience though. As you said they work fine in your vehicles so maybe it's hit/miss. Also never had an issue with short lifespan out of the NGK's except on my turbo 318is that I run a rich tune on. Lifespan on that car is 15-20,000 miles. 50,000+ on all our other ones.

To each there own. Honestly I could care less about what plug was in my e53. I just went off real oem. My piont was, his brand new plus 4 plugs are not causing the miss fire, unless one is damaged. Using a plus 4 plug will not cause a miss fire.

Can anyone elaborate on how to gap a 4 prong plug?

The only thing you can do is a visual check the gap on multi prong plugs to make sure they have not been dropped in transit after they were packaged. I have never seen a gap spec for them and every manufacturer has their own version of these things. They are sold as a long life feature compared to standard plugs. This technology is 15+ years old. The Plug manufacturers have moved on to single side strap/ground straps and precious metal plugs like Iridium etc.

There is a fine wire gaping tool which can be used to established a baseline. See the plug factory rep for any insight. I was a Champion Spark Plug Factory Rep for a few years and the lab testing completed at that time showed no value to multi prongs over single ground straps. The claim on multi prongs is a longer life and more consistent plug gap growth over time. Now that precious metal is used in the center electrode and ground straps, that value point is muted. See lab tests for answers if there is any :dunno:

BMW installed them at the factory for YEARS. Now they have moved on. It is just a piece of technology locked in time. Either of these plug types will fire and allow the vehicle to perform as engineered - naturally. The fine wire one just provide a little better idle and tip in acceleration feeling compared to the multi prong ones.

The OP has a misfire at idle. Only two things can cause that issue. Fuel (right mix) or spark. His only changes were valve cover removal, (Potential vacuum leaks) and ignition issues (Coils, Plugs, Coil/Plug Boots (Wires), Ground straps, electrical connections, etc). The recommendation is to review the install of these items and CONFIRM that they are indeed OK. New plugs are 99% ok out of the box. 1% died in transit by being dropped, stuck in oil/dirt then installed etc. Coils die from being over heated and or electrical shorts. A volt ohm meter will confirm windings are not shorted but that test will NOT confirm coil output, only a test with a lab scope will confirm total coil out put. And NO, the visual test of the little blue spark is not a test, its just a good guess.

See Bosch Fushion, and others images below. I have also attached some really bad plugs images that are multi prong plugs for those who think adding a prong solves oil fouling and poor fuel issues......:rofl:

Sorry for the rant on plugs and coils. One too many "bench racers" arguments over the years with techs and self proclaimed experts at race tracks in my Champion and Engine management years.

Awesome info Stephen. I might try some iridium plugs, just for kicks, in my Z:)

I believe my issue has to do with the boots on the coils, not vacuum leaks, lean fuel mixture or anything like that. The car has 126K miles, it was running perfectly fine. I was doing a valve cover gasket, since I bought the car last month, did not know the story behind the plugs, I decided to replace them.
As soon as I started it ran funny. I hooked up the code reader, it says multimple misfires.
Today I bought a set of BREMI boots and a set of NGK Iridiums.
I should get it next week. I will post the results here once I install it.

I think your on the right path....