I have a 1993 non-turbo 300ZX that is having a tough time idling down when coming to a stop. It will fluctuate between 400 and 1200 rpm's, and sometimes seems hesitant when taking off. Had a tune up done in February. Died on me one time last week after getting off the highway and pulling to a stop, but it did start right back up. Hasn't happend since then. Appreciate any help, thanks.