I've tried the +4s twice now ( I'm a slow learner).. Both times, I had rough idle issues..
I tried it in my Jeep, and Buick.. I won't try them a third time...
89 300SEL Money Pit
92 Blown Buick Ultra Pimpmobile 220K and adding 1K per week
88 Wagoneer Slightly modified (Not for soccer moms)
04 Kia Sedona with every option... NICE