I used the +4's and didn't like them. The fact that I never checked the gap on them might have had something to do with it, but my 951 had a bit of a hesitation after I installed them, and I changed them out again after a few thousand miles for single electrode bosch platinums that I believe run a bit colder than the +4. I gapped the single electrode to .030 and the hesitation stopped and the car ran 100% better all around. I've heard of BMW guys having issues with the +4 plugs as well.

 

I might just have to try changing plugs. I got the Bosch +4s because the local Carquest just happened to have them in stock. The car had NGK Iridiums in it when I bought it and it ran horrible. Many people have told me the 944s don't like NGK plugs.

But I'll try switching to conventional Bosch plugs.

 

Insert obligatory side-gapped spark plug joke here.