Yeah mike is correct. Most 16v engines should use heat range 6 for spark plugs. I have tried (rare) 7 and the (bad) 5 from NGK. Not good. Still 6 is the best.
What mike tries to say about the feeling is, like the engine no power, and response is weaker. Also notice knocking is sometimes more apparent. Should happen for EFI engines, but it does because of incorrect heat range.
I do recall Chin saying 11 (gap) for 20v and 6 (heat range) for 16v. Here is 1 NGK sample,
http://www.ngk.de/uploads/pics/ZK_Grafik_waermewert_02.jpg
http://www.ngk.com/images/NGKsparkplugNum.gif
Hope this helps. But for many of us, just a refresher course. hahahaha.